If you rule out the physical, then its down to the mental part of the equation.
You can take your lack of "sexual appetite" very seriously
or make a game out of it. A game is much more fun.

-- But I don't want to play, I don't feel like it.

Yes, that's the point. He wants to play with you.
So if you need help getting in the mood, then let him give you all the help you require.

You don't have to be horny to make love or have sex.
Just enjoy the moment, the touching, the feeling, and the sensations
of giving each other pleasure.

Being in the moment is an art form.
It's very hard to concentrate on one thing - sex with your partner -
when we've got a million things on our to do list that aren't getting done.

We all go through phases where something that used to be a big turn-on
isn't anymore. Give yourself permission to find out what your current thing is.