You should note that the existence of dark energy is deduced indirectly from motion of celestial bodies under the assumption that the standard general-relativistic theory of gravity holds. Also, and this is a more general point, educated specialists in any field—not only physics—aren’t stupid and really know their field. Therefore, if you, as a non-physicist, can come up with a simple theory of gravity that is not believed by the physicists, the theory is almost certainly false—somebody certainly had the same idea long ago and there were reasons to reject it. Keeping this in mind can save you a lot of time and futile effort.
For reasons why your theory is false please follow the link in Mitchell Porter’s comment.
You should note that the existence of dark energy is deduced indirectly from motion of celestial bodies under the assumption that the standard general-relativistic theory of gravity holds. Also, and this is a more general point, educated specialists in any field—not only physics—aren’t stupid and really know their field. Therefore, if you, as a non-physicist, can come up with a simple theory of gravity that is not believed by the physicists, the theory is almost certainly false—somebody certainly had the same idea long ago and there were reasons to reject it. Keeping this in mind can save you a lot of time and futile effort.
For reasons why your theory is false please follow the link in Mitchell Porter’s comment.
A better attempt at gravity-without-gravity