What should I do?

This guy and I were dating for about 8 months and over the summer I heard a rumor that he kissed my best friend. He wouldn’t answer my phone calls, texts, and would hide in the back when I visited him at work. In August I finally got to ask them both about it face to face but they denied it. So I let it go and the guy and I just drifted apart, but this last week, the girl comes up to me and she starts crying. She tells me that the rumors I heard were 100% true and that she was really sorry. I absolutely believe her because she isn’t a person that cries very often. I just don’t know what I should do. I’m afraid he will just lie to me again. Please give me your thoughts. Thanks!!