Liking someone who has a girlfriend?

So I like this boy who has a girlfriend a lot I used to have a crush on him when I was 12 but nothing happened then because we were both young and it was a silly crush he moved away and I forgot about it he has moved back recently and I really like him he is in one of the same fitness classes as me so I see him 2 hours 5 times a week and recently I done a competition with the training club am in and he was there but with his girlfriend and she seems really nice and I know I should t do anything and need to back off so I have tried to and am not speaking to him as much in the fitness classes but he is messaging me a lot and he has become friends with two of my friends during the after party of my competition and there is a group chat and everyone is getting on and my friends have invited him and his girlfriend out more often so I see him a lot I don t know what to do I also think he might like me but I wouldn t want to break him and his girlfriend up but at the same time I wouldn t care if I did and I feel awful it is ridiculous I m 20 and I have never liked someone this much we have lots in common and it is making me feel awful we both have a competition in a different city next month and me and him are the only ones from are class going so I m going to be with him for 2 whole days and I just feel crap I m thinking of telling him how I feel and saying I need to not be friends with him or back off away from him for a bit I don t know what to do