I'm just going to throw down what I think here. It's really great to hear that you are a supportive girlfriend. Most girls these days absolutely cannot stand when they're away from their bf whether he's traveling for work or not. I don't know how many times he has done this in the past, but from what I can say right now, these sort of things happen in every relationship at some point, people aren't perfect, sometimes our selfish sides show, and we end up deciding to go with what's not as important, rather than what actually is important. The important thing in this situation is you and the concert he promised to go to with you, and the un-important thing being the rave.
I am pretty dumbfounded as of how so many of these people on this forum can just outright say "Dumb his ass" just because of this one situation, it makes me wonder how long their past relationships have lasted. But like I said before, I have no idea how many times he has done something like this so if I read wrong and it's actually been several times, then I stand corrected. But by all means, I'd say you just have to trust him sometimes, and give him space. You don't have to go everywhere with him, and I'm sure he'll be fine. A DJ getting shot is pretty unlikely considering they're the life of the party, a rapper getting shot on the other hand...yeah I could see that happening only because it's happened tons before. But really, anything could happen anywhere, so try not to worry so much. But back to the situation, what you really need to do is sit down and actually have a serious talk with him and tell him that what he did is immature, in a relationship, promises are very important, and not keeping them could be very damaging. It's probably not a good idea to think about marriage if this is a re-occurring issue, but even if it isn't you should let him know it can be very damaging in relationships.
And about the the whole "Getting famous thing" It's a bit risky but dreams are awesome, I'd tell him not to put his future on the line for the chances of that happening though. It's great to hear you both are in college though.