Formetosee~
This may sound like coming from waaaaay outta left field, (and it's just a suggestion.. & many may oppose this immediately)....but, the first thing that came to my mind is have you ever considered a third party inclusion?
From the sound of your bf, he has little, if ANY interest sexually, and because he didn't seem too "put out" over you having an outside affair, just maybe he'd be good with a third inclusion? JUST a thought.
By no means am I encouraging infidelity. I'm talking about a mutually concented inclusion.
For most, those kind of arrangements don't work, but who knows?
Talk to him. What can it hurt? If you're good with it, maybe he might be, as well. And who knows....maybe it just might be enough to stimulate him back into satisfying you. Anything's possible...
Shangrala
Good luck.