Hello MomoBear,
I don't really have much advice to help you, but I wanted you to know you are not alone. I could have written the exact same post (in fact, I'm pretty sure I did a long time ago...).

I did some work with a therapist on this and it became about interrupting the cycle. If I could feel myself start to spiral out of control, picking silly fights, getting caught up in the past, I'm supposed to try to interrupt the train of thoughts. (Note the supposed to... It's really hard!) When we were long distance, this would take form in getting off the phone and then calling him back half an hour later or so when I was calm, and talk about what happened. Now that we live together, I try to leave the room and distract myself (usually with PC) until I'm calm and can go cuddle with him. I also try to journal a lot when I'm upset.

Lastly, and probably most importantly, I try to have plenty of calm conversations about what is going on in my head. He knows that I still worry about things that happen in the past, and I know that we can't change what happened in the past. We both try to do things to remember and show each other why we're together and why we love each other.

Feel free to PM me to vent if you need to; I understand where you're coming from.

Good luck!
Ro