You know a good friend of mine told me at the time my xh left that the sex in MLC is largely in their heads! At the time I thought he was wrong, and now I am not so sure.
One of my friends whose xh had (and is still having) a MLC - one of the slow ones(!) discovered later that the woman he left for he stopped having sex with when he moved in with her. Nada for at least a couple of years. And he left for (among other things) a better sex life.
It makes you think just how much of a fantasy world they inhabit