RSD triggered by breaking up with the guy I never loved

I never digged into rejection sensitivity before my last post: https://www.reddit.com/r/adhdwomen/s/gmYjD0bQg6

So I dreamt about breaking up - we broke up - and I want to stalk his computer (to know if he cheated or has someone new), want to arrive to his apparent, want to write “sl🙃t” on his car. I am so so hurt (while glad I got rid of him) and I feel betrayed and the last time I was grieving breaking up - it lasted 3 years.

I can’t bear these emotions anymore, I am tired of crying.

what can I do?

UPD: he confirmed cheating