This may be about your own boundaries. Boundaries are about knowing what is us, what isn't us. I think for some of us who are empathetic, we do consider what others say about us, but some people are disordered.
Borderline is named for being on the border of what was known as neurosis and psychosis. Someone who is fully psychotic is more obvious, but for pwBPD- feelings can feel like facts. So if they feel something - they may in the moment believe it's true, even if it's not true.
I know someone who sadly aquired schitzophrenia. If she says something like a person is shooting radio waves at her, I know that isn't true, and her saying it doesn't make it true. But when someone with BPD makes a false accusation or statement, it could be just as false, but not sound as obvious. What can help here is a stronger boundary- what is true about you, and what isn't.
If your ex called you a pink elephant, would you be ruminating over it, wondering if perhaps you did something or didn't do and you might be one? No, you are certain you aren't an elephant. You wouldn't be wondering.
Now, substitute "pink elephant" for the accusation of keeping him from his friends. You know that neither of these statements are true. You don't need to give them any more thought or defend them.
In my own experience, when I realized my BPD mother could say things that weren't true, I was shocked. In my own mind mothers don't do this. Why she did, I don't know but if she thought something, it seemed real to her.
If I could step out of my emotions, I could see where I could do or say something and she'd experience it in a completely different way. One example was when she was getting some construction work done in her basement. I had just had some work done in my house and had cleaned up the construction dust from it. I casually mentioned that she might want to cover a bookshelf in the basement as it would be a lot to clean up. I didn't mean literally- she is a short person- she'd have to ask the workmen to do it but that wasn't how it came out or how she heard it.
What she heard was that I ordered her to climb up a bookshelf, which was not feasable or safe for her. I would not ever have even thought that. This resulted in her getting upset with me, and accusing me of telling her to do that.
You probably never even thought about keeping your partner from his friends but if he thought it, he believed it, even if you did nothing of the sorts. This is disordered thinking. We can't control that. What you need to keep a hold of is your own reality. It's not true and him saying it isn't true.
Sometimes we just can't ever know what someone else is thinking but we can decide for ourselves if it's true or not.


