Feeling heartbroken

My ex and I were friends for a year before we dated for three years. We then were friends with benefits for a year after we broke up. We were talking about getting back together when suddenly he told me he wanted to go date one of our mutual friends. He said we could still be friends but I told him I couldn't do that and cut him off. It has sucked so much. I miss him so much. I see him with this other girl sometimes and I hate it. I just want someone to tell me he will regret it and come back to me but I don't think he will.