Your ex is a history lesson, not homework you have to keep turning in.

What ended still has something to teach, and it stops being useful the moment studying it turns into a daily obligation. Going over the same scenes for the sentence that would have changed everything is not analysis, it is a way of keeping the relationship open. The lesson is finite; the rumination is not.

Write down what you actually learned, in a few plain lines, and let that be the record. When the replaying starts, notice it and put your attention on something with a next step. Time does most of this work, and faster when you stop supervising.