Duty sex - advice needed please

Ok, so my wife (LLF) and me (HLM) have a pretty good marriage. We both do equal shares of the household work, I get home from work earlier so I do a bit more for the kids, I do the cooking, she does the laundry, we share the cleaning…you get the picture. We don’t have any major fights and I we love each other.

We both are still very fit and spend quite a few hours a week exercising, as we did when we first met 20’years ago.

Our sex life has been pretty good up until recently, once a week (due to work and the kids), more when we can do. But recently, she’s just being going through the motions.

About 5 years ago I mentioned something to the effect of ‘If a couple aren’t having sex, then one of them will be probably wishing to be sleeping with someone else’

It was just a comment, but now since her libido has dropped, and she’s giving me duty sex and I think it’s down to what I said. Duty sex feels horrible.

I ask her all the time if she still loves me, she says yes. Also she tells me she does at random times, we are still affectionate etc..

Anyway, I am planning on asking her something along the lines of ‘Are you still happy when we have sex?’ Or something like that. I’m kind of worried about the answer, but still.

Does someone, anyone have some experiential advice? I don’t want to make her upset.

Any help would be greatly appreciated.