It is my belief that the only difference between good friend, even fantastic friends and being a couple is attraction.
There are many reasons why I fell out of love with my ex husband, even when I was VERY proud of him and we were best friends for a few years after we split. But I was no longer attracted to him and despite the friendship, complicity and the rare occasions we had sex, he was no longer my partner, just a good friend.
We split, because someway we both had started living one day at a time, I don’t know about him, but for me being in such relationship was killing me inside. Never looked back, getting divorced was the best we could do for each other. He is now with a woman who fancy him and I am no longer taking care of a friend/little brother. We both agree the only regret is not splitting sooner.
Best of luck in sorting this up, I do think however that you don’t need to put up with a sexless marriage, if this doesn’t work for you. You seem to be doing all the right things without success, it seems the only thing you can do is accept things are the way they are or leave and find someone else as she doesn’t seem motivated enough to do absolutely anything about it whatever valid or invalid reasons she may have.