Sounds a lot like what happened to me 10 years ago, after 24 years of marriage. What it may surprise you to discover, as it did me, is that it is not as uncommon as you may think.
Of course, everybody's story is different, and only those concerned know the full details, but sometimes one partner just "goes off the rails" in some way for no good or apparent reason and refuses to listen to anybody, and in the end, there is nothing the other partner can do but stay civil, be there for the children if any, and move on.
However, while scars may remain, wounds do heal in time, especially with support from family and friends.
Although divorce was the last thing I ever expected or wanted, and I did everything I could to avoid it, 10 years later my new life with my new partner is better emotionally, intellectually, and financially than my first marriage ever was.
Sometimes an old ruin becomes the foundation of a new mansion.