I'm sure a lot of couples end up like that. You start off as lovers, then spend decades as sensible bread winners and parents, the children leave - and you can't get back to being lovers again. You're just not the same people.
If you're generally happy, secure and content, perhaps that's enough. If you're deeply unhappy, you might leave. Maybe you'd prefer being alone or with somebody else? It could, perhaps, be a risk worth taking.
Why not ask him how he feels about the situation? A chap at work said the love had gone from his marriage. He felt incredibly lonely - but would never upset his kids by leaving.
He fancied a 'little fling'. I said 'No, thanks' - being past the menopause and no longer interested (at all). It simply hadn't occurred to him that his feelings might change dramatically if he became involved with another woman - typical!