Liking a girl?

I'm currently in a relationship with a man but have been having feelings for a girl friend of mine. we are good friends and trust eachother very much. we've never done anything together, but there is something there. I feel like I'm crushing on someone I shouldn't be (not because she's a girl but because I feel like I'm cheating). I'm so confused and I haven't confused anything to anyone, not even a friend. just felt like I need some insight or better yet perspective on this.