If he doesn’t want to hold your hand in public when he used to before.
Or give you a little kiss now and again for no reason.
Or buy you a bag of malteasers (or something else thoughtful you’d like within the budget) just because he thought you’d like them,,,then he is not really interested in you or your feelings or making an effort for you.
He is either taking you for granted because you’ve been together long enough that he thinks you’re both set for life and thinks you feel the same as him, and feels he doesn’t need to do anything else other than live in the same house as you because you love each other so that’s fine and that sometimes he fancies sex and thinks you’ll feel the same as him so that’s all fine...
Or he really doesn’t give a shit about you but stays for his own convenience/because he believes in marriages lasting/some other reason about something you bring to the relationship (money/couldn’t afford to live in the nice area without your half of the mortgage/security and mothering him/cooking cleaning etc).
It may be a pattern he’s fallen into over the years or could be something that he’s gone off you for. Like losing respect for your political views or something, or because you didn’t lose baby weight or something else ridiculous but he’s never said to you, but sometimes he wants sex so he uses you for that even though he doesn’t physically fancy you...
It’s difficult to know without you speaking to each other. A frank convo would be the way to go. To see what he feels for you. And if he still loves you then he needs to know to show that by the little things, otherwise how are you supposed to know.
And sex without any other feelings for me would be a no-no in a relationship, it’s just usury.