Girlfriend Refuses to stay in uni house because of spat with housemate

My girlfriend recently came to stay over, and my housemate made it clear he was not happy with her staying there. I did give him loads of notice, said we wouldn't get in anyone's way, and it was the only way we could see each other on her birthday. This really upset my girlfriend to the extent she doesn't want to stay over again. The summer ball is soon, however she refuses to stay at my uni house and wants to pay over £50 each to stay in a hotel for the evening when I have a perfectly good house to stay in for free. In my opinion I had every right to have my gf round for a few nights so i could see her on her birthday, and that my housemate has completely over reacted. However, i believe my girlfriend has also completely over reacted, and doesn't want me to socialise with my housemate and doesn't want to stay at my house. I am upset that my housemate caused my gf to be upset but i can't understand why my gf cares so much that my housemate didn't particularly want her there for no reason other than they have rubbed each other the wrong way up before. I don't want to pay extra for a hotel, i am a student and skint as it is. Any advice? I can't refund the summer ball tickets either. Thanks

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