I don't really have any experience in relationships, but I've heard of two methods to help stop intrusive thoughts.
One of them is the thought-stopping method. When an intrusive thought occurs, you immediately imagine a big stop-sign with the word STOP! on it. It is also okay to switch the current thought for another thought that isn't upsetting.
Another one that I've heard of is called the rubber-band method. You wear a rubber-band on your wrist and whenever an intrusive thought occurs, you snap the rubber-band.
Those are two methods that I know have helped some people, and it might just help you too. It might not work, but it's worth a try if you're willing
Glad to help!