It's not sociopathic not to believe in being a martyr.
You have a CHOICE. Either sex is important to you, or it's not. If it's not, it's a non issue, you dont' have it.
If it's important to you, and you don't fancy your partner anymore, and your sex life is dead, then why stay and be miserable? If the OP is only 40ish, that's a lot of years to be without a great sex life!
When I say, you move on, I didn't mean you pack your bag, say bye and drive in the sunset and you know it. But I stand by what I said, if the relationship is dead, you move on.
it’s a perfectly normal thing to lose attraction
it's also perfectly normal to still fancy your partner like crazy, and even more when you both know what the other like and you are very comfortable with each other.
Neither are wrong.
It's staying despite having no attraction any more AND complaining about it that is stupid.