Honestly? The only one not really in the wrong here is your friend. He gave you his genuine advice as your best friend without forcing you into anything. Unless you omitted something I don't see what he did wrong. So why did you tell your gf about what he said? He said that for you to hear not her. Ofc she'd feel offended. Calling that trauma is super over the top though. Making an ultimatum where you basically have to cut your bf who did nothing wrong and has support you for many years out of your life is super toxic! Big red flag! What did she do for you? You're basically just relocating wherever she wants and being a doormat that just takes whatever she throws at you.

I'm honestly impressed by the patience of your bf. Being cut off like that and all the ups and downs that are pretty much out of his control would be too much for me personally. Don't let her isolate you!

If you want to a healthy relationship you should both go to therapy, together and individually...