Confused...sorry for long post

I was with my now ex boyfriend for about 6 months when I found out he had asked another female for nudes about two months ago. We argued for about a week and went back and forth until we finally decided to end it. Meanwhile during the relationship, my cousin had always been a problem, causing arguments and being messy. Anyways, when we were arguing, I found out that they had been having many late nigh, long phone calls while we were still dating. We got into an argument and it ended with her saying that she would never stoop low enough to date him. Flash forward a few days, she tells me she has feelings for him and when I confronted him about it he says that it’s normal and whatever. The ended up getting together and are still together now. Meanwhile, I meet this great guy and he ends up taking me to prom about a month later. We’ve been together for almost three months and we’ve gotten really close. During the day, I’m all happy with him and everything’s great. But at night, when I’m all alone, I still think about him, my ex. I loved him and he was just snatched from me within a really short time. And I tried to fill that hole that he took with anyone else, and now I’m afraid to hurt him, my current boyfriend. I don’t know what to do anymore. I just hurt.