As others have opined, despite the august accumulated wisdom of all the best and the brightest here, this is not the place to come for relationship advice. (Or maybe sometimes not even boat advice ):lol:
It is a place to have some fun, shoot the breeze, and share ideas.
A few thoughts...
1. If your marriage is truly seriously stressed by having that boat, maybe a little marriage counseling?
2. If her primary complaints are things are always breaking and needing fixing, how about a smaller, newer, easier to take care of boat? Especially if you are in your, ahem, 'senior' years (which it sounds like you are), how much use will you really get going forward out of an older, 50 ft boat needing a fair amount of maintenance? Maybe life might be easier for you, and more acceptable for her, with a boat that's easier to take care of.
3. As others have suggested, try to accommodate her desires. What does she want as much as you want a boat? If you can find a way for her to have that, she might be more accepting of a (smaller and easier to own) boat for you. And just maybe even join you on some trips.
Just my 2 cents, and certainly worth much less than that.