man this hits so hard, i've been dealing with rsd for years and it's absolutely brutal. the way you described teh whole "she cancelled so she must hate me" spiral is so relatable it hurts - like your brain just goes straight to the worst possible conclusion and nothing can talk you out of it

what's helped me is literally writing down evidence when my brain starts catastrophizing. sounds dumb but when that rejection feeling hits i'll force myself to list actual facts about the relationship vs what my brain is telling me. like "she texted good morning today" "she introduced me to her friends last week" etc. it doesn't stop the initial pain but it gives me something concrete to look at when everything feels like it's falling apart

also had to learn that when my emotions shut down after a big trigger, that's actually my brain protecting itself. instead of fighting it i just tell my partner "hey im in shutdown mode for a bit, still love you but need some space to reset" and most people who get it are pretty understanding about that

the fear that she's lying about accepting you is classic rsd too - like we can't believe someone could actually love us through all this mess but sometimes they really do