Hello Tupla,
Wow... "Former best friend" is right. All of that is a lot process, I imagine. So sorry to hear that is how things turned out.
When you say - "It's doing a number" on you - could you say more about that? I hear that you might be ruminating, which can be really annoying.
Hang in there. Reach out any time.
Rev
It happened last night. I woke up at 2am from a dream where she confessed to cheating on me for about 50 times. It was awful to wake up to that dream, it felt so real. When you're groggy and barely awake it can feel like it actually happened.
In the morning I had a dream where the friend was dodging my questions but finally blurted out he needed to "step in because you were being abusive towards her". I know that's not true but it hurt nonetheless.
I had been having really unnerving flashes of them having sex earlier but the actual rejection and infidelity took a longer while to start processing in my mind. All the little things lining up, painting a terrifying picture.
As a sidenote, my ex showed me the 1981 psychological horror film Possession, and even during our r/s I thought about how the movie chillingly reminded me about the nature of our r/s. Afterwards, knowing about the infidelity, it got even more poignant. It's still the single most disturbing cinematic experience for me. It is about the ravages of divorce, but I've seen other people mention it as also portraying a r/s with a person with BPD.