X and I had a heart-to-heart yesterday that left me in a difficult place. Most of our play time sessions go like this: he takes care of me, I tie him up and do other things to him, we have sex (but he doesn't finish) and I finish him with fellatio. It works for us as a routine, but it also means we haven't tried any other positions in years because he's usually tied up by then. And missionary is pretty impossible if you can't move your arms or legs.
So what I asked him was if he actually likes coitus. He never finishes (although that's also a question of being paranoid about pregnancy) and it goes on for as long as I want. He said he doesn't mind it, but it's not his favorite, no. So what do you do with a partner that doesn't like "sex"?
1. Acknowledge that sex is more than just coitus. There is so much more that can bring pleasure. There's kissing and petting. There's manual. There's oral. There's nipple play and butt play. There's BDSM play. There's reading each other erotica. There's masturbation (mutual or otherwise). There's watching porn. There's a whole lot of things one can do that are "sex" without being a penis in a vagina.
2. Acknowledge that it's okay to be selfish. He doesn't mind it, but I like it. So why not keep doing it? It's a service to me that he doesn't mind doing. So it's okay to keep indulging.
3. Focus on what other things you like to do together. X is great with his mouth, something I don't take advantage of enough. One thing we used to do a lot of is he'd lie on his back, I'd sit on his face and pin his arms down with my knees. I get oral pleasure, he gets a little bit of bondage, and everyone wins. We should do that more often.
For me, the most important part about sex is the connection I feel with X and being close to him. If the coitus isn't that great, that's okay! We can still be there for each other in other ways. He's still a caring and loving partner and I wouldn't trade him for anyone else.