Hey Steph – thanks for your question.
You know, lots of different thoughts go through our minds when we're about to lose a real friend, to changing circumstances. But the real issue here is why you wouldn't want to be with your boyfriend for support, as well as being his girlfriend?
Fly to Vegas. If he really gets his heart broken to someone that isn't within his control, that's fine. Prove you're the better person to be there for him as you should. Chances are, this is just some infatuation, if anything. From what you say, it's likely only one-sided anyway which will be a great opportunity to talk more about it with him.
Grow out of insecurities and into strength within, to make YOUR relationship into what you want it to be.
Does that make sense? Let me know if you need clarification on ANYTHING though too.