TLDR: love my gf but we have started fighting too much so taking time out, her sister has called me toxic before, now her sister angry reacted to a meme my gf reposted about missing someone, am spiralling over it.

My girlfriend and I both have BPD. We had an amazing start to the relationship, meshed so well, I met her sister and she really liked me.

Then, things got bad, we both got bad mentally and started fighting horribly.

After one big fight, we made up, and she gave me her old phone as mine broke. When I went to set up my WhatsApp I saw her texting her sister with screenshots of our fight and the sister replied "toxic gf anyone?". I lost my shit because it felt like the end, like now everyone in her life is against me and there's no point staying together. I got pissy to her about it, she lashed out at me again for overreacting and blaming her for something that has nothing to do with her, I let it go.

We are currently not talking for the next month as the fighting got too bad and honestly I'm really questioning if we should ever start talking again because I'm in a state where everything about her annoys me and I feel like I hate her. However, I've been trying really hard to stop and to think more clearly.
Then, today, I saw on Facebook that she reposted a meme about not being able to stop thinking about someone and her sister angry reacted it.

Now I kind of never want to make up with her again. I know she didn't make her sister do that, but they're very close, and I feel so uncomfortable and angry. I know the sister has to take her side but I feel like I'm being made into a villain and the whole thing is forever ruined and there's no point trying to fix anything since her sister will always make her against me in these situations.

Does anyone know how to see this in a more rational way? Or do you agree that maybe since it has gotten this bad it's best that we never talk again?