I am so sorry to hear that. Sincerely. I am.
You're very, very right. I've been in relationships before where the other partner suddenly decided sex wasn't for them. Either I promptly left those relationships or found other arrangements outside the relationship.
That's sadly a choice many people are forced to make and no one will be worth trading in my sex life, as I've been always up front about the fact that I would never just let it die.
A couple of questions, even though I'm absolutely sure you've tried everything. Have you read the work Mating in Captivity? It's absolutely vital, an incredible read, though I'm sure you already have.
Your partner might do well to read it if they haven't. It opened my eyes to a lot of things.
I'm very, very happy to see you have the option to open up. A lot of people don't. Personally, I've been doing ETM since 207 and never looked back. I couldn't be happier. Currently, we're polyamorous, and it's been the best relationship I've ever had.