Like other posters have mentioned, it generally isn't something that starts out like that and when you've been in a relationship for a very long time there are a lot of other factors to consider other than just sex, like kids, living situations/money, social status, other forms of intimacy, etc..

We don't have a dead bedroom, but I do have a partner that's asexual and it's not easy. When we started dating things weren't nearly as bad as they are now, but things have changed as she's gotten older, processed some childhood sexual abuse, and been on medication that fucks with her libido. We have sex, but she would be perfectly fine never having it which makes things tough.