Ruminating, imagining, and rehearsing arguments in my mind. How to stop?

I had a bad end to a friendship of 16+ years. We had many long talks and heated texts and our official “end” was about 3 weeks ago. Yet I am in my head as if it’s happening NOW. I’ll get ruminating thoughts about what I could have said, or rehearse what I already did say, or will say in the future, or re-play the same memories and “evidence” in my head constantly.

I am EXHAUSTED. I don’t want this for my life. I want to drop it and move on with my life (therapy, extracurricular activities, work, etc.) and I’m trying, but my OCD is getting in the way making me ruminate and it’s a compulsion thinking about this friend.