what should I do?

when I was a freshmen, I was dating a guy for almost 2 years. we broke up. I cared about him a lot. 5 years later I started talking to him again, but theres one problem. I have a boyfriend right now, and we have been dating for 2yrs and a half. im thinkig bout breaking up witth him, and go back with my ex. but what should I do?