There are a number of things that highlight the fact that the end of this relationship will be better for you (maybe even both of you). First, I only know one couple who got together young an "made it". Although their relationship isn't that great now. Most relationships that start young are doomed to fail because neither person has had enough life experience, and both usually have to "find" their true selves to some extent. Second, you say that this has happened before. Twice, as a matter of fact. That isn't good, obviously. Either he cannot handle pressure/stress or he has taken those two other events and tried to purposely use them as opportunities to break up. In both cases you don't need to be in a relationship with this guy if he ditches the relationship whenever something comes up. Lastly, DO NOT, I repeat, DO NOT go for the whole "I want us to stay friends" bit. MissAnn hit the nail on the head. All that will mean for you is lack of closure on this failing/failed relationship while he moves on. He will treat you as a friend (and even that is debatable) until he wants to fu*k you or until he dates/fu*ks around and returns to you later. Don't settle for that. Stay broken up, and let him go to his next school. You should spend some time single, hanging out with friends. Do things that you couldn't do while you were in a relationship. I'll further say that even if you meet someone soon who genuinely seems nice or "right", don't date them for a few months just so you can be single for a bit and get over this guy.
...one can be sure of nothing until it has already happened...