Feeling like a third wheel...but I'm not the third
(I may be in the wrong thread but I'm having a difficult time identifying what this is...)
For context, my girlfriend (Bi-F) and I (Bi-F) have been dating for 4 years. We get along well and are very satisfied with each other and the relationship we have built. She requested we start finding a third FwB about two years into our relationship and I was unsure at the time. (I had never actually been with a guy before)
She recently found a third on Tinder, and met up with him alone while I was on safety duty. Everything went great, she came home safe and told me about him. She met him twice after that before I finally got the courage to join. It was a lot of fun and we all got along great at first. Recently I noticed he has been messaging her more, touching her more and leaning towards wanting more from her. She is totally not interested in a relationship, just wants benefits. I on the other hand am a little more emotional and like to know I'm wanted where I am. Having a connection, no matter how small, is vital for me to feel comfortable.
Without getting into the nitty-gritty, I am feeling like the third wheel every time we meet up as a group due to a general lack in atmosphere and a disconnect between me and him. The two of them share a lot of similarities and connect really easily. They have similar styles of humor. He has mentioned a few times that she was his type. I don't always feel left out, he does try to accommodate me. He answers or reacts to my texts, he turns his attention to me 40% of the time, and hes really sweet most of the time. I would let them meet up without me but my partner's whole goal was for us to almost always be a trio. She said she would break it off with him if we couldn't make it work.
I'm not sure if this is common for ENM/monogomish/open relations? Should I just get over it and have fun? I know that it's impossible to be completely equal and yet I have this feeling like we are a Polaroid in an art museum.
TLDR: personal insecurities making me feel like a third wheel with our FwB.