My best advice would be to get into counseling with an ERP therapist who specializes in OCD if you haven’t already. This issue is very unlikely to improve on its own without treatment, but it is treatable. Regular talk therapy can actually make OCD worse, so be sure to find someone who does Exposure and Response Prevention. If this is tough to find, you can use NOCD, as all their therapists use ERP. I use NOCD and am happy with my treatment. If therapy isn’t available due to money/ insurance, an ERP self-help book should work. I’ve just never used one.
As for the present moment,
just try to notice and acknowledge the thoughts and feelings and try not to do any of your compulsions. Just let them be present and sit with them. You don’t have to like them or think they’re comfortable, but sit with them and just let them be present in your mind without entertaining or answering them. Over 15 to 30 minutes, you should see your anxiety decrease. If you’re doing this for the first time or for the first time in a while, your anxiety may actually increase, which is fine because your mind is used to the compulsions being performed for that short-term comfort. Just sit with the thoughts, not engaging and not answering or dwelling on the questions; doing that will only reinforce and feed the ROCD. Just respond “maybe that’s true, maybe it isn’t.”
Keep in mind, as well, that rumination and breaking up are also both compulsions. Other compulsions that are common can be reassurance seeking (including from yourself) checking and questioning your feelings, examining your partner for flaws, mental reviewing of feelings or things like it in the past, rating your partner or your interactions, comparing them to other people, etc.
This is a good read: https://www.treatmyocd.com/blog/relationship-ocd
Most importantly, try and give yourself some extra self love and patience. It’s extremely crucial that you be a friend to yourself and be as gentle and compassionate as you can to you. You wouldn’t be cruel or hard on someone who is really struggling, and you deserve that same kindness.
Nobody beats this overnight. But you are seeking help and trying to do what’s best and that is respectable and admirable. You are giving yourself the best shot you have and trying to get better. A lot of us on here have the same worries and fears, myself included, and if we all help each other out, it may become a little easier. =]