Usual warning: mobile device and raw emotions. Please give kind advice

Ughhhhh.... My heart is broken. I originally started dating my bf, Alvin, almost two years ago. Within a few months I was also dating his wife, Brit. I was head over heels. They also have a young daughter who I grew immensely close to.

Me and Alvin clicked right away. We have the same style of communication and share many hobbies together. We went on many trips together and we have never once raised voices. It's pretty amazing.

I had more trouble connecting with Brit. She went through an emotional time period. She broke down at one point and we took a short break from everything. She started going through therapy and approached me shortly after asking to "start over." I was over the moon.

I gave her and Alvin lots of space since some of her stress came from me always being around. And I would make them meals, invite her on outings, etc. But the more I asked to be connected, the more I could feel her pulling away. I wanted to be involved. We called our relationship a triad. To me, that meant being intertwined. She didn't want that.

Then she broke up with me because of all this stress it was putting on her. My heart still hurts. She's a wonderful person and I didn't want her to feel like she was. I want to give her space but now I'm not sure what to do about Alvin.

I want to still be involved with him but I can feel this is a watered down version of the relationship that I really want. Alvin has suggested (multiple times) that I get a primary. Then that primary could fill the voids he is leaving. But I don't want some washed up version the relationship that we once had. I'm already not invited to their daughters events or family dinner.

I am feeling like an accessory to Alvin's life instead of a full partner. Losing all three of them is a devastating thought to me. But I don't know how to move forward. I let myself become too enmeshed and de-escalating is not what I want.

I'm sure some SoPo people have been through this. Any sage wisdom?