I haven't read other replies yet because what you say has resounded so much with me. My life sounds very similar to yours.
I told my husband, but he never really did anything about it for years - because he worked away from home and wasn't around to see it. (He has since admitted that he felt guilty and powerless at the time because I had no other source of support while he was away).
Anyhow, I sucked it up for years and kept my feelings to myself. Until finally, children fully grown adults, FIL died a few years before and MIL started rapidly declining, I couldn't cope. DH was retired, his siblings - living miles from us - spent a great deal of time telling DH how to provide care (mostly taking it all on and not spending money), I just broke. I could not go near MIL - I didn't even go to the funeral or meet the family when they all descended - I could not be at home so took my tiny caravan 2 miles away and lived there for about 2 months until it was all over.
DH visited daily and we were OK because he understood that I needed to get away from his stress. By leaving him to it, he only had himself to deal with and didn't need to feel that he was neglecting me. I was as supportive of him as I could be - actually better, removed from, rather than being directly involved in, the situation.
I saw a counsellor and worked through my feelings but it took a long time. The whole experience has changed me for the better, I think, but I have come to realise that things were left to fester for too long. I gave so much over the years, with little return so I eventually had nothing left.
So this is something of a cautionary tale. Find a source of support, please. A therapist would probably be best, and these days even in the UK it is very difficult to find free counselling - but not impossible. Don't let it go on as long as I did.