I'm still feeling new to this forum and a bit timid about offering advice to others who probably have more experience than me. But, I can relate a bit to what you are going through Night Dragon.
Last year, I moved in with a man. When he and I met, he was sleeping with a woman. The three of us hooked up and she stayed lovers to us both. She's gay, in a relationship with a woman but likes to sleep with men. There is no romance, but a lot of care between her and her friends/lovers.
Very soon after I moved in with him, he crashed. No idea how to describe it. He'd sleep 16 hours + at a time. Stopped going to school. Couldn't help out with much of anything. Some days, couldn't form complete sentences. He'd stumble on a word and then get upset because it wouldn't come out making sense. He'd sit against the wall with a mean, evil expression on his face, as if he was ready to go out and murder someone. It scared me!!
He was needing the kind of support I was not able to give - especially since I'd moved to a completely new place, didn't have a support network of my own and had actually expected to lean on him a bit to settle in.
He would compare me to our lover, saying literally, "Why can't you be more like 'D'?". Well, hon, she's not in love with you, first of all. Second, she doesn't live with you. Third, you are not projecting major, intense emotional and psychological stuff onto her. And fourth, I do say the things that you are requesting of me, (the ones that she says), but you react completely differently to me when I say them.
So... all that to say... sometimes our needs just can't be met by some people. And often not because of the person, but because of the dynamics and triggers that come up between people.
Anyway, I think I'm going a bit OT, but I just wanted to say that on some level, I understand. And I hope things settle into a good place for all three of you.
My heart is too big to fit into one person.