Trips without SO

My friend group (7 Males and 2 Females) asked me to go on their trip they are planning together for a week. I think it would be really fun to go with them considering I don’t see them much. The problem is my girlfriend (19F) is in a schooling program where she can’t miss days. So she won’t be able to go. I am 20M and we have been dating for 9 months. I’m hesitant to ask because I feel like a fight might start because of this. I have a feeling she is going to say it’s stupid and say how she is going to be working all week while I’m out (that has been said before when bringing up the idea of trips). Is it selfish for me to go without my GF? AITAH?