I'm not sure if it is the problems of living with the same person. I suspect that actually, disinterest in sex is pretty normal. I suspect it because the nurse-practitioner whom I see for female-parts stuff told me that quite a large number of her patients didn't have sex at all, or had it only rarely, or wished that their partners wanted it a lot less often. I figure she knows, 'cause asking people about their sex lives is part of her job and they've got a vested interest in being honest with her about it. With everybody else in the world, I bet those people portray their relationships as a lot more sexy. My own marriage is not very sexy, but people tend to presume that we are setting the bed on fire every night, because we are very affectionate.
I think that just not being interested in sex is like not being interested in sex. It's not on your mind. I am sure you can see intellectually how sex is actually pretty boring. Maybe you remember from being a child. Though my experience is, when I was a kid sex was much more interesting, because it was taboo. As an adult I know enough about it to know that it's nothing much worth thinking about, really.
But one can, and I do, have the experience of feeling horny but not in response to anything in particular, and not having some sexy image in mind to go along with the feeling. An undirected in-the-body horniness. Or there's the non-oriented sexuality sort of experience, where the desire to have sex has little to do with anything that's sexy per se, rather it's a desire to maximize intimacy and one wouldn't really care if that's achieved by genital contact or cuddling or by tickling your beloved's brain with a feather or some other mode of expression that may or may not exist.
