What would you do in this situation?

I met what seemed to be the perfect guy over 5months ago, it's easy we connect without problems, we always have something to talk and laugh about, we're extremely attracted to each other and basically there is no work to make it the best. A month ago, an ex calls him (he didn't specify exactly what she wanted) and he started distancing himself from me. We talked about it and he said he didn't want anything to do with her, it just was a shock from the past. Yesterday, I found out that they still talk, he said mainly about work and life. He said this woman broke his heart 6 years ago by leaving him for another man, but he still has some underline feelings for her. I'm not sure what I should do, because I know I'm a better woman for him, only because I truly care about him and she already hurt him. 6years is a long time to be apart, I'm just afraid that I'm going to get hurt in the end. Why is it people go back to they're ex's? When they have something so good in front of them?