I am no longer attracted to my boyfriend, now what?

My boyfriend and I have been together for over 2 years. When we first got together we were in highschool. We followed each other to college, but once there I felt we were headed in two different directions. We have always been very open to getting married after college, and we even got promise rings over a year ago. But recently I have felt unconnected from him, I am no longer sexually attracted to him, and there are very few times where I look at him and find him attractive. I have thought that it maybe because he doesn’t pull his weight in school, and it bothers me that he is not trying to better himself. I just don’t know. Regardless I need help- I have a history of cheating on my boyfriends but him I dont want to do that to. I have already turned down 3 different guys at my school, and that was a big deal for me considering my cheating history. Help me, please!