I think the “getting your needs met by one person” thing is more of a failure mode of bad monogamous relationships. As you mentioned, it’s especially a problem if a person has varied sexual needs, as those are things you’re only allowed to get from one partner in a monogamous context, however a common failure mode of monogamy is to also expect your partner to provide for all social needs.
I think for different types of monogamous relationships this also varies. For instance there’s a thing called “emotional cheating” in which partners don’t have physical relationships with the opposite sex, but have a particular type of a emotional closeness that people are only expected to get from their partner. This can be an example of the failure mode.
I think the “getting your needs met by one person” thing is more of a failure mode of bad monogamous relationships. As you mentioned, it’s especially a problem if a person has varied sexual needs, as those are things you’re only allowed to get from one partner in a monogamous context, however a common failure mode of monogamy is to also expect your partner to provide for all social needs.
I think for different types of monogamous relationships this also varies. For instance there’s a thing called “emotional cheating” in which partners don’t have physical relationships with the opposite sex, but have a particular type of a emotional closeness that people are only expected to get from their partner. This can be an example of the failure mode.