Is it normal to be obsessed with my boyfriend's ass?

I have this crazy obsession with my boyfrind's ass. Its not like I want to do him with a strap-on or anything. I just think his but cheeks are so sexy and would love to play (like press on) with his hole and lick it. I've played with him in the bath but I would love for him to considre it as normal in our usual sex life but instead he's uneasy and freaked out by it. I try to be understanding and try to respact his wishes but I even get jealous when I read about how many guys like it when their girlfriends do it or how many guys want their girlfriends to do it. I used to think its awkward too but with him I feel different. Is it normal for a lady to feel this way about the subject?