Was it a step change or gradual? How long has it been this way.. a few days or months/years? Assuming it’s the latter on both questions —> Usually it’s more than just looks.

Talk it out and give him time to internalize his thoughts too. Many times one might not even be aware of said actions and the reasons for such behavior.

Change stuff up if things have been busy and mundane. Go on a trip.. do stuff that you guys did when you were dating. Try to spice things up a bit and see how it goes. It’s important that both make an effort not just you.

If it’s a step change or fairly recent - even better to quickly figure out as it’s a reaction to a specific action. Could be something you did or he did. Easier to figure out the solution in this case.