I am obsessed with my girlfriends ass

I'm not sure if it is a full on obsession (that's what I'm not sure of), but I definitely think about my girlfriends ass, a lot!

She has a large, curve, and tight ass. She doesn't think it's all that good looking, but I do and I have tried to tell her--but thats not what this post is about. In short, ever since I have first seen it, I have this odd fixation with her ass: I have a need to grab it, spank it, and just can't stop staring; it enters my thought whenever I think about her. Am I just attracted to my girlfriend, or is this an actual obsession? Will she think I'm a creeper if I tell her?