If you messed up a potential relationship with someone you really loved and now they are in a new relationship do you tell them you are sorry for what

You did (not to try and get them back just to apologize and explain why u acted the way you did (because they hurt you(not intentionally)and that you didn’t mean to hurt them because you really feel bad about the situation) or do you let it go and live with the guilt and eventually you’ll probably move on from it?
(emotional hurt)