We’ve been together almost 6yrs and have toyed around with an open relationship. We have sort of a cute old married couple dynamic, and not a great healthy sex life. He wants to explore sex with other people, but needs some feelings involved to feel comfortable. I’m fine with that, and that’s the same thing I want to do. But he has found someone and I have not yet, and they have very intense passionate feelings for each other. Very infatuated and lots of wanting. I have never felt that way about anyone. Infatuated, yes, but not this drug-like wanting feeling he describes. He likes her a lot and wants to treat her well, to the point of being extremely boyfriend-like with her and doing crazy things he’s never done with me. But he maintains that he likes feeling like that but will always choose me over anyone else because of what we’ve built and how amazing it is.

He also thinks that in the long run, he would consider being polyamorous with her. He would still marry me, but would be equally close with both of us.

My instincts say “fuck no, end this now, this is supposed to be casual, not a second girlfriend,” but can I learn to be okay with it? I want him to be as happy as he can be and while he won’t be miserable just being with me, he wants more that I don’t think I can give. Is there any way I can learn to be comfortable and not hurt by him being poly? Do we have to break up? Please share perspectives or experiences.

TL;DR my bf really likes this other girl he’s seeing and wants to treat her too much like a gf for my happiness, even have a future with her as well as me. Is there any way I can figure out how to be okay with that?