he has a girlfriend

So there's this guy I have had a crush on for so long now, but this year I moved over to an independent study so when he messaged me to hang out I was really surprised and of course said yes, well of course some sexual stuff happened and after it was already finished he told me he had a girlfriend and I feel so terrible, should I talk to her about it or just leave it be, it's not that I don't want to tell her I just don't want to start problems for myself when I return next year.. It's already going to be awkward enough seeing them together, any advice???