I think it’s hard to judge these situations without knowing the nuances, which proves difficult even for those involved as everyone has a different point of view
Is it possible that from this girls perspective, she is just trying to be a good friend? You mention his anxiety - is she acting this way because she cares about him? He might get defensive when you try to talk about it because he sees her as a good friend and thinks you’re unnecessarily jealous. I had a similar situation years ago, and in hindsight I can understand why the girl was apprehensive about the relationship and protective of him
Equally, it’s possible she’s deliberately crossing the line. Some people just like to mess with relationships, some are actually interested in the person. Maybe she’s just messing around because she doesn’t want him to have a girlfriend as it takes his attention away from her - or maybe she’s recently discovered she has feelings for him
I do think you need to insist that you have a conversation about this with your boyfriend. Ask for honesty, don’t get bitchy, stay calm, promise not to flounce off. Listen to his side of the story and ask for him to do the same for you. A relationship will begin to break down without good communication so this is important, and should help you decide what you want to do next
I’ve been in a situation where my partner was too close to another woman. I tried to be reasonable about it, though the lying and his apparent ignorance to what was going on sometimes made me frustrated and unreasonable. The relationship had other issues but it was easy to target this one. Eventually I gave him an ultimatum, but while he chose me it didn’t feel like a victory and I left soon after for other reasons
I wouldn’t advise giving an ultimatum, in any circumstances. For one, it makes you look like a controlling partner (which arguably would be true). But more importantly, you shouldn’t need to give him an ultimatum. Anyone who truly loves you and wants to be with you won’t need an ultimatum; they will see when a friendship is inappropriate, understand why it’s upsetting you and resolve the situation with their friend
So after your conversation about why you’re concerned, there should be one of two outcomes:
1. you understand that their friendship is innocent, you trust your partner, you begin to work on accepting the situation, he tries to understand why you might be worried and puts your mind at ease, perhaps he tells his friend to tone it down a little if necessary
2. you are still suspicious of her intentions, you don’t trust your partner to resist (because he’s complicit - if you trusted him, it wouldn’t matter if he lived in the Playboy Mansion). He doesn’t understand/care about your worries. She keeps overstepping the mark, unchecked. You still feel anxious about their closeness
In the case of #2, I would say to leave because that’s not conducive to a happy relationship. You shouldn’t want to be with someone at the expense of your misery - you need to love yourself more than that. I wish I’d known this at the time but I know in that situation, you feel threatened and want to cling on to the relationship. But there’s no point in clinging on to a one-sided relationship
