In my case, I let it go on for nearly 10 years as it got worse and worse, so that by the time I left it was maybe once a year and even then only if SO had had a lot of alcohol. It sucked. I finally left. Now at least I'm not getting any (coming up on 5 years of that, pun intended) BUT isn't as incredibly upsetting/depressing/unfulfilling as being married and still not getting any. Use the old Ann Landers test - are you better with SO and no sex or without both (at least for a while)?
(Signed) Not anonymous this time but I don't blame you one bit!