I'm sorry you are having such a difficult time with this. Hopefully you were able to resist the urge to "drive down there.") You asked for some tips on how to make "it" stop (presumably your thoughts regarding your ex's going out with someone else.) Unfortunately there is no way to make thoughts stop that I know of. The key is to learn to allow them to come up (because they're going to anyway) & then let them drift away at their own pace without getting hooked.

Here are links to 6 articles, from PC's archives, that offer tips for coping with obsessive, intrusive or just plain stuck thoughts along with a link to an article on the subject of rumination & one that talks about how to sit with painful emotions:

Coping with Obsessive Thoughts

How You Can Overcome Intrusive Thoughts | Dialectical Behavior Therapy Understood

7 Ways to Stop Obsessing

Some Ideas to Help Stop Obsessing

5 Ways to Free Yourself From Dark and Obsessive Thoughts

https://psychcentral.com/blog/9-ways...tuck-thoughts/

https://psychcentral.com/blog/8-tips...dium=popular17

https://psychcentral.com/blog/how-to...nful-emotions/