Which should I do? I'm stuck between a rock and a hard place.?

I joined the U.S Army a few years ago. And just recently got the rest of my enlistment bonus. What's cool is I already have my own place, have a nice car, and I'm pretty good financially. So I was going to spend most of it. The problem I made was I made a couple promises that I shouldn't have. My friend of 20 years. (I'm 26 so is he we have been friends since 1st grade.) Transferred to UCLA out in Los Angeles, to get his masters. (were from Pennsylvania). I haven't seen him in exactly a year. Last June he came back and we all got together and it was good times. And ever since then I promised I would make it out there to L.A and visit him. Now the other promise. I Just recently made the mistake and promised my girlfriend that I would take her and her younger brother to the Penn ST/Alabama game this September. Her little brother is a HUGE PSU fan and her and I both are too. He has never been to a game. He joined the army to but he leaves for Basic a week after the game. So her and I both thought it would be cool to go to Happy Valley see the game, party and stuff as a "going away/good luck" type present. What should I do? My friend out in LA keeps writing on my facebook wall and stuff telling me how much fun were gonna have out in LA, and IDK. I only have enough money to do one or the other. Any advice? I gotta break the news to someone, who should it be? How should I do it? It's going to be awhile before I'll ever get the chance to go out to LA if I don't go now, but my g/f is not only going to get pissed at me for backing out, but her brother is so stoked to go, I would feel like a d*ck if I just said no were not going. Please help.