My SO likes butt play

My SO likes butt play. And I mean really likes it. I've heard about guys having a g spot there so it's not uncommon for them to like it. But lately, it's like he doesn't get as in to sex without it. It seems like he's not as turned on without it, and it's not the same if I don't do it to him. He's been with a high number of women and I don't think he's interested in the other sex. Should I be concerned or is this normal?