It's hard man. I was like that for so long. It was like I had to tell my girlfriend (at the time) every ruminating thought I was having so I could just stop obsessing over it. I started taking a medication for it that did help a bit and after a few months I didn't need it really. I also just got better about trying to focus on other stuff. For the first time in years I've been pretty bad about it again for the last 2-3 months. Every embarrassing thing I said while drunk when I was 18-19. Rude shit I said needlessly. What made me a bad boyfriend. What made someone a bad girlfriend. Thinking about past conversations wondering if an ex did cheat on me like my friend accused her of. Some days I feel like the only respite is being too busy at work to think about it or just having fun hanging out with someone. Sometimes i just start focusing on something that happened however long ago so much that I can't focus on my book or game or whatever else. Sorry, I don't really have any advice for you. Just relating. Try to just enjoy the little things as much as you can I guess.