I'm glad you keep posting your story and I appreciate reading it. Your story has stuck in my mind since you first posted here.
I totally sympathize with what you're going through. Guilt is a hard emotion to deal with.
It sounds like Alex is trying really hard and is making a lot of progress.
But I'm still sad for Alex too. She deserves to have someone who is as excited by her as you are by K.
The "cuddly, dependable teddy bear" comment seems to capture the heart of it. Alex knows you feel that way about her; you know you feel that way about her. I can't imagine spending the rest of my life with someone who feels only cuddly with me but crazy-in-love with other people.
You wish Alex would try dating other people herself so she could experience the thrill of having those feelings. But, in the first place, she's been so broken down by her struggle to make things work with you that I can't imagine she has any energy left to try dating others (even if she weren't oriented towards being mono).
Secondly, what if she does meet someone else she's compatible with and with whom feels all those in-love feelings? If that happened, wouldn't it make more sense for you and Alex to separate and each go off to experience your various loves?
Or would you stay together no matter what? Do you want to grow old with Alex? Maybe "cuddly teddy bear" feelings are the secret to growing old together, and those tender feelings will outlast the rush and physicality of new love.
I don't know the answer to these questions, and I have no idea what I would do in your place.
But I still worry that the underlying issue is simply that you and Alex aren't right for each other. You said originally that you and Alex weren't really sexually compatible. I know Alex struggles with being sexually open--but maybe there is someone else (or some other type of person) with whom she could be more sexually open.
There might be circumstances in which two people who aren't sexually compatible with each other could still be happy in a primary relationship together. BUT it has to be special circumstances.
The two people have to agree that they aren't sexually compatible, that they are more cuddly/best-friend-ish AND that's the way they want it.
Then they can both have other relationships to explore/satisfy their separate sexualities. (Or, if one partner is more asexual and happy being mono, the other could have outside relationships).
But they have to be on the same page about it. It sounds like Alex really longs to be sexually compatible with you, and doesn't understand why she's not. (Maybe she's never been sexually compatible with anyone, and it's a source of great pain for her).
Sorry--I don't mean to bring discouragement here when you and Alex have made so much progress since last fall.
It just makes me sad thinking of her point of view.
On the other hand, I think she's totally unreasonable about the showering rule. It's like telling you that you're dirty if you see other people. It's almost like punishment.
Single, straight, female, solo, non-monogamous.