I'm not sure if it's going to help much, but you might want to look into trying to write down jealousy situations? What you've felt, why you felt it, and try to see if you could have misinterpreted something (even if you're sure you haven't, think of it as playing devil's advocate against your feelings).

For ressassing things over and over, try to set up an "alert" system with friends, where if you seem preoccupied, they should remind you not to. Treat it like a bad nervous habit, get distance, and look at it only once you're calm and sure it can't affect you as strongly.

You can also distract yourself by trying for the opposite feeling that whatever you're thinking about brings up; if it gets you angry, try watching something scary, if sad, try something that makes you laugh, if it makes you feel bad, try something that makes you feel good?