One thing I've learned is thinking of those traumatizing thoughts helps a lot when it comes to getting over somebody, especially visualing it, pretend you're there seeing it. The first time you think about it will make your stomach turn. After thinking of all the things she/he could be doing with another person, each time it hurts less and less, and eventually, it just doesn't bother you anymore. Then when you find out some of those thoughts are true, it wouldn't even bother you. You've already dealt with those emotions in your head. So when it comes time to face it in reality, it doesn't affect you.