How do I become comfortable with relationships again?

I have had three bad relationships in the past 4 years. First used me, second forced me, third cheated on me.. I was just wondering what you would do to overcome all the bad stuff that has happened in the past? I now like somebody, and he likes me aswell but I am having a hard time excepting that he likes me. Also he says he would never hurt me like the others how can I come to believe him?