This occurs when we don't love ourselves for who we are and so we look for validation from others, but unfortunately, the validation isn't always good. Until you find out who you are and actually love who you are, you'll only be attracted to those that don't or cannot love you the way you want to be loved. You are subconsciously thinking that you aren't lovable so you accept relationships with someone is incapable of truly loving you. In case you haven't been told lately... you are a gift from God, and he doesn't make mistakes so you are wonderfully made and you deserve someone wonderful... so go find him! There are good men out there.