I think it’s not necessarily just a cultural template; there are some aspects of standard romantic feelings and relationships that can make a high level of emotional intimacy more likely. Many people are afraid to be emotionally intimate, lack the impetus to change the status quo, or don’t even realize it’s something they want. I think sex acts as an important catalyst for vulnerability in romantic relationships: people are driven to have it independently of interest in intimacy, but it can lead to greater intimacy regardless. You’re showing somebody your naked body, accepting that you might make weird noises or faces or do something you normally wouldn’t, potentially falling asleep next to them, etc.
As an illustrative example, the main character in a romance novel I read was nervous about having sex with her partner because she felt insecure about him seeing her body (fear of vulnerability), but was too horny to let that stop her. Assuming sex with your partner ends up feeling good and safe, you trust them more and are more willing to be emotionally vulnerable with them afterwards (of course, people do not in fact always feel comfortable and safe after sex; as a simple example, maybe someone’s partner’s first words to them afterwards are, “man, you’re really bad at that”).
Supposing the book character (and real people with a sufficiently similar psychological makeup) also feels afraid to be vulnerable with friends, she might not get the same “push” to do something that changes that—horniness is a powerful motivator, and there might not be an analogue for the sorts of activities that might lead her to feel more comfortable being vulnerable with her friends. She might grow closer to her friends over time, but people usually have to be friends for far longer to achieve a similar level of emotional intimacy to what they could get more quickly in a romantic relationship.
I also think people have a greater desire to learn more about their romantic partners, to “know and be known,” and so on, than they do towards their friends. This could in part be cultural, but not necessarily in the sense of conforming to a social script, and there could be an innate element as well. At a basic level, when trying to woo somebody, it makes sense to get to know things about them—inviting someone on a date that you expect them to especially enjoy is good for your romantic prospects. If you’re interested in making major commitments with the other person (e.g. starting a family), it’s natural to learn about their ambitions and approach to life; monogamy (which might be inherent to some degree, though there’s definitely a cultural aspect) also seems like a driving factor, as it’s only wise to ensure the quality/compatibility of your sole long-term partner.
People also tend to want to spend a lot of time around their partners, and living together often feels like a good idea, for reasons going beyond cultural expectations (e.g. you like to fall asleep cuddling, which natural leads to spending nights over). The more time you spend around someone the more emotionally intimate you’re likely to become; living with someone helps as well because you end up seeing their domestic foibles, interacting with them before they’ve had coffee, and so on. Again, this doesn’t work if you cannot, in fact, stand the way they live; disputes over things like mess levels and chores are a leading cause of conflict in romantic relationships. The claim is not that romantic relationships are necessarily more emotionally intimate than friendships (obviously untrue), but rather that they have more potential to be for most people, especially in a short time frame.
Interestingly, while people usually try to have good experiences as a way of bonding with their friends and partners, taking emotional intimacy as one of the core things that makes a relationship good suggests that bad experiences could work better: you see and interact with the other person when they’re stressed out, angry, humiliated, crying, vomiting from food poisoning, etc. Now, in some cases you might find each other intolerable under these circumstances, which I suppose means you’re not cut out for that level of intimacy with that person—which is fine, relationships based solely around casually hanging out or having pleasant experiences together aren’t necessarily bad.
However, it does seem like a good idea to at least be deliberate about what you want from your relationships with different people and know how close you want to be. I suppose people don’t tend to explicitly seek out bad experiences to have with other people, but I think it’s an element of why people like to go on adventures together: there are bound to be problems and things you didn’t anticipate (e.g. running late, bad weather, flat tire), and those can serve as bonding experiences.
Disclaimer: I want to start by saying that, since this is a hard subject to discuss precisely and we might have slightly different vocabulary, I might be going full steam down a side path and at some point in this comment miss my exit. Also, some of the things I say might be annoyingly obvious to you, but I thought they were worth mentioning in case they aren’t.
You said in the original post that you wanted to better relate to other people, which seems vague because you don’t specify what you mean by “better” (by what criteria? what are you looking for?). However, assuming you want things from relationships that are similar to what other people usually want from relationships, my guess would be you wish you could more deeply connect with other people and maybe you feel a sense of alienation/loneliness. I can imagine someone feeling similarly unfulfilled if they only hung out with literal cats, even if they liked cats and had access to books.
Usually feeling isolated means feeling like you don’t understand other people that well, and/or like they don’t understand you very well, but in a specific sense. There are probably some ways in which you understand the average person better than they understand themselves or better than other “normal people” understand each other, but there’s a difference between being able to predict their behavior or knowing what factors led them to be the way they are (e.g. having more knowledge of evolutionary biology) and relating to them emotionally.
To some extent that’s a difficulty shared by many unusual people (e.g. veterans, expats, people with strange personalities), but I also think it’s sometimes possible to emotionally relate to people more if you try to think a lot about them and make analogies between things you feel and things they feel. For instance, I’m not a drug addict, but I have on some occasions stayed up very late playing Civilization V while my inner homunculus tried and failed to get me to go to sleep instead, which is sort of similar in some ways to being a drug addict.
Another approach to relating to other people is to change things about yourself; if you became less ambitious you’d probably feel more emotional resonance with unambitious people. Likewise, if someone thinks of themselves as the victim of their circumstances whereas you take responsibility for rising above any bad things that happen to you, you could relate more to them if you started thinking of yourself as a victim of your circumstances. I think people sometimes do this, but I would guess you are not very open to that sort of thing; I would less confidently guess that you don’t want to deliberately become more normal even in ways that don’t affect your productivity in order to relate better to other people.
There’s also the flip side where other people don’t understand you very well, and probably often don’t make that much of an effort to understand you better, which I suppose you have less control over. The second one especially seems hard to influence; maybe you could ask people to try harder to understand you, but I don’t know that that’s likely to work. It’s somewhat possible to find common ground where other people can easily understand you (e.g. I like spaghetti and many other people also like spaghetti) and put in deliberate effort to “feel seen,” which might work to varying degrees.
I think the upshot is something like, if you are feeling a sense of alienation/loneliness from lack of deep mutual “understanding” (in the sense I described it), there are probably ways to reduce that without compromising your values, but I’m also not sure how feasible it is to make it go away to a fully satisfactory extent. I believe the common wisdom is that it isn’t, and that the only real solution is selecting better people to connect with.
Also, I think sometimes when people are talking about empathy they’re referring to a sort of emotional porosity that doesn’t route through conscious thought (e.g. feeling in higher spirits when you’re in a room full of people in high spirits); you didn’t mention anything like that, so I’m not sure much you experience it or know about it. I think sometimes this is a quality people like in others, and which enhances bonding. I don’t know how much this can be deliberately controlled (to some extent it might be down to neurotype), but I do notice that when I’m at a rock concert I can either choose to get “swept up” in the collective excitement, or to hold myself apart.
It also seems possible that your relationships with others are less good than they could be because of interpersonal mistakes you make—I wouldn’t know, because you don’t really go into details on things like how you treat people you view as moral agents vs people you don’t; if it’s basically the same as how you’d treat a cat I think people might reasonably take issue (also this is sort of a nitpick but “moral agent” seems like a strange word to use in this context because you talk about whether you see people as bearing responsibility for their own happiness, but it seems weird to call failing to be as happy as you could “immoral”—I’d intuitively just call that something like “agency”).
Some examples: say Alice and Bob are friends. Bob believes he knows more about Alice’s preferences than she does, which may or may not be true. He might sometimes insist that her stated preferences are wrong, and be unresponsive to her claims to the contrary. Alice probably finds this very frustrating, especially if Bob is in fact wrong. Part of the issue is that Bob isn’t modeling her very accurately, and I suppose part of it is that Alice wants to be seen as an agent—but it’s in the narrow sense of wanting him to believe that she’s capable of knowing her own preferences.
It’s also possible that, even if Bob has a relatively good idea of what Alice prefers, or a better idea than her of what’s “good for her,” she’d rather have the autonomy to make her own decisions—even if those decisions end up leading to less happiness for her; she’d rather he didn’t override her autonomy whenever he has the opportunity. This is probably a situation where Alice would feel like Bob doesn’t “see her as a human”—with the reason maybe once again being that Bob is failing to model her preferences. However, it also seems possible that maybe Bob is well aware that Alice places more value on autonomy than some notion like “welfare” but doesn’t see that as important—in which case maybe it’s more about what he values. This seems more like something to do with “respecting boundaries.”
There could be this additional (perceived) violation where maybe Bob thinks she would benefit from going to therapy for some issue, but she’s not very receptive to the idea. She might disagree that she actually has that issue, or maybe she isn’t open to therapy for whatever reason. Bob is able to come up with schemes to get Alice to go to therapy without her realizing he’s doing so (like, getting her mother concerned about her wellbeing, watching a movie with her that he claims he’s interested in purely for its entertainment value but which promotes the idea of going to therapy, etc.). I think if she found out she’d be upset in this “I’m not being seen as a human” way, and it seems similar to this sort of manipulative element to people often treat cats and children (which seems probably fine for dealing with cats but maybe bad for dealing with children—at the very least I sometimes noticed my parents were trying to do this sort of thing to me growing up and I think they probably shouldn’t have).
(Also, sometimes people manipulate children or cats not for the child or cat’s benefit but for their own convenience, which seems worse.)
There’s also an only somewhat related phenomenon where Bob positions himself as the “authority” in some sense and enforces that through a power differential; if Alice perceives this as unjust I think she might feel dehumanized in some sense. To give a clear example, when I was a kid my father would often criticize my taste in movies, video games, music, etc. in a very dismissive way. I wasn’t really able to fight back or criticize his taste in turn, even though I think (even looking back on it now) his criticisms were in fact often based on a flawed understanding of the things I liked, and in cases where there were actually issues with my favorite media there were similarly egregious issues with his favorite media.
This dynamic was enforced through a disparity in how well I could articulate my thoughts vs how well he could articulate his, and through the power he had over me as a parent who could punish me for things like “disrespectful tone”; I found it very upsetting. Going back to Alice and Bob, I think Bob can enforce a similar dynamic solely through superior intellect, ability to think quickly when stressed out, etc. (and sometimes this sort of thing happens in real life), though it would probably be more difficult.
To be clear, I’m not accusing you of doing any of these things, but it seemed from what you’ve written in this post and the previous one that sometimes there’s an element of interpersonal conflict or other people being upset with you, and the things I listed are broadly elements of how people frequently treat children and cats. It seemed worth mentioning in case you do behave in these ways sometimes, or in case other people perceive you to be.