This sounds relatable. I was Leigh when I first entered my relationship with my partner. I'm not really polyamorous by nature, I don't think. But I was willing to do it for him because I knew he loved his other partners and because it wasn't fair to him or them for me to try and break them up. But it was a struggle. I might be totally pro polyamory in theory. But back when I had anxious attachment, I would be seeing my partner as The Person that I loved the most and wanted to spend the most time with. And I would feel that he saw me as One of Three. It's not fun.