Trust Issues

Mariah
My boyfriend and I have been on and off for 1 year & 5 mo. We've broken up or just stopped talking to each other way too many times for me to count. One of the main reasons for that is because people like to lie to him and say I'm doing this & that. & he NEVER came to ask me about anything. He just had sex w/ different girls because he felt it was justified. (I heard about what he was doing and had to hound him for the truth) He has never yelled at me or blew up at me , but the things he says are what get to me. The last time we broke up he told me that he only agreed to be with me because he felt bad that no one liked me. Now.., this was a year ago.., but I remember it clearly & still remember crying my heart out in his room.. It still hurts like a bitch. Since then he's been trying to prove to me that he loves me and that he's serious about us. I love him so much and I want to trust him so badly but I'm scared.. Am I being a bad girlfriend? Should I already trust him?