I (32F) have been seeing my partner, S (37M) on and off for a few years, but in the last year it's gotten much more serious. S has a wife, and another girlfriend. The wife and I get along and have no issues. The girlfriend and I have never met, but there's a lot of insecurity. S has helped me a lot with my insecurity and I've deliberately worked on it, so I'm no longer insecure, but I am starting to resent her.

Girlfriend has been around much longer than I have, and up until a few months ago, I don't think he really told her much about me. He's admitted to slowing things down with me because he feels protective of her and her insecurity. A few months ago he was reluctant to add me on social media because he didn't want to upset her, and it took him over a week to tell her about a step up in our relationship, one that I was excited to tell those closest to me. It really hurt that he took so long to tell her. She's been upset and insecure since she found out, which has been having an impact on him and he hasn't had the emotional energy to interact much with me.

I've spoken to him about it, but he's quite protective of her and I don't know how to express it without coming across as an insensitive bitch. I don't know whether this is just a part of poly where our relationship is constantly impacted by other partners, or how to deal with my resentment.

This is my first actual poly relationship with other partners involved so any thoughts would be hugely appreciated!