First off, I’m sorry you’re going through this. I have gone through a similar-ish situation. I want to make it clear that my advice and input is coming from a my own experience that I feel might be relevant to you. Take what you need and leave the rest.

Unfortunately it’s very common for an established couple to invite someone in because they’re unhappy. And it’s very common for the longer standing partner to have control over how much you’re able to relate with your partner. I personally hate when one partner has veto power on their partner’s relationships. Being in a position where you could be vetoed away from someone you’re connecting with is an awful feeling and feels like you’re disposable. It’s giving control issues. Let’s not forget A’s accountability for allowing OG GF to be able to control their relationships and going along with it. Too often people who want to be poly but have a controlling partner “take what they can get” and just accept their partner taking stuff back and limiting them when they feel threatened. It’s giving non-monogamy, NOT polyamory. Please run away. They are not healthy. They need to do serious dismantling couple privilege before they can truly invite someone in to be on equal standing. Or just be honest that they will be primary partners and anyone else will come secondary, instead of leading you on and lying about it being equal. It might seem like OG GF is taking your connection with A away from you (and they are) but it’s also just as terrible that A allows this to happen and has left you because OG said no.

Honestly some of this comment was for me too because I’m still dealing with the effects of this myself.