Difficult. My partner was dysfunctional (as in not wanting sex) in the past, but that was with a previous partner and not with me. Now I'm the one who has no interest. We don't talk about it either. But then I've recently concluded that we don't talk about a lot of things, only that this is my point of view. From his, everything is going well except that he's waiting for that miracle one day that his wife will be all into him again.
He will sometimes make a comment to which I usually reply that the problem is not that I became asexual, but that I don't want to have sex with him. Not that he gets it, and I'm tired of sitting him down and saying 'we need to talk'. It bothers me a lot though that we are not intimate.
But in essence, Esposa has the better answer. It's all about communication.