Ex drama

So I broke up with my ex a few months ago due to the distance as I was away at college and thought it'd be better for both of us. We'd been dating for 15 months. I told him it might be possible for us to be together again in the future once I've adjusted to college and everything. I tried to stay in contact with him and stay friends. I came back home for break and asked him if he was over me and he said yes, which is fine, even though I still had feelings for him. I then found out he now has feelings for one of my best friends. I've never felt so hurt in my life. She was always friends with both of us and hung out with us a lot. It makes me feel betrayed and angry... I want to get over him but don't know how.. What should I do?