Just friends or not???

Well, I recently became very good friends with this person that I go 2 school w/. We are very compatible and we get along so well that some people around me are actually asking if we two are going out, which I always laugh at politely and say no. I began to crush on him a few months ago and while I wish it was possible, I know that a relationship with him is just not going to happen any time soon, because the thing is he's got a girlfriend! I respect that he's in a relationship with a great girl (for quiet a long time now). I also realize that he and I are two very flirty people and we usually end up play-shoving each other in the hallway or walking to cles with each other (our cl shcedules are very similar). How do I determine if he and I are just friends or if there's something more? He's very attentive to me and to tell you the truth but I don't want to cause a rift in his relationship with his gf by taking this too far, even if I try to resist.