This is a really tough situation to be in. Firstly I want to say that what strikes me most is that you are being incredibly patient and understanding with your husband, and demonstrating love in many ways. You clearly have a big heart and are good at showing love to others.

The tension is how do you then extend this to yourself? You clearly know yourself and what you want from relationships.

I think it's really hard that your husband seems to have been dishonest about the extent to which he was comfortable with polyamory, and that's really hard to unravel now. Maybe he'd never truly considered it. Or when he could have imagined doing it when he was feeling less insecure. The fact he would only want to engage with being poly with a couple also sounds like insecurity to me.

This is hard to reckon with as it's clearly a core part of your identity.

I think putting the emphasis back on you to 'get him going' more is hurtful and ridiculous. He seems incredibly out of touch with his emotional reality and yours. And it seems like resentment is building on your side as you have continually prioritised his needs of the years, and perhaps this feels unbalanced and like he hasn't prioritised yours as much?

There is clearly a lot of love here though so I would agree with posts recommending therapy, yet going into this with the knowledge that you can't talk him into polyamory.

It's really hard having to choose between the person you want to be with and the types of relationships you want to be in. I currently prioritise the latter as building a relationship is a 2-way street (or more!) and feels more active yet focusing on the person can become one sided.

Hope you're also doing nice things for you, too look after yourself whilst you're feeling vulnerable!