He helped you come out of despair and low self-esteem? I don't mean to sound harsh, but that may be part of the problem. Relying on others to make you feel good or banking your self-esteem on how others view you/make you feel. I know that it's impossible for anyone to avoid having at least part of their self-image dependent upon how others view them, but the vast majority of your self-image should come from yourself. As I said before, work on having the bulk of your positive self-image come from within. Don't rely on others to bring you happiness. This is not to say that other people can't make you happy, but your relationships should not be the "end all, be all" of happiness in your life. I would seriously recommend talking to a therapist about exercises and skills you could do to develop and improve your self-esteem.

In the meantime, don't let this guy continue to hurt you. Try to keep yourself busy and distracted so your thoughts don't stray to him so much. Let him go so you can heal and begin to love yourself. Don't let the way he has treated you make you think that love and care is not meant for you. The way he treated you had nothing to do WITH YOU. It sounds like he was just an ***hole, pardon the language. That doesn't reflect on you. You say he dumped you? Well, dump HIM from your thoughts and your life. I know it's not easy, but, with time, it will get easier.