I had false memory about a real event. I started officially /boyfriend girlfriend/ dating my now husband in July of 2020, however, in June , we were " dating" but we had not had the discussion of being official. So at some point in May or June, i went to an old friends house to watch a movie and some kissing and pg-13 stuff happened. No sex of any kind but actions that would still be considered cheating. I NEVER gave this any consideration until April of this year i had a thought pop up out of the blue " what if you did that stuff like a week before you became bf/bf" which felt like cheating.... it felt SO REAL. i became obsessed with trying to figure out the exact date this movie night happened so i could feel better. I even confessed to my now husband who took it a bit hard ONLY because of my behavior. i made it seem like a big deal so he assumed it must have been one. I was able to get past this with the compulsive idea of " well as long as it happened before we were official, its ok, i can let it go" and that worked for awhile, until BAM new OCD idea of " well, what if it actually happened RIGHT AFTER you became official and you just don't remember?" and when i tell you that NUKED me..... I went thru old phones looking for proof of when the event happened, i even reached out to the old friend to ask ( keep in mind that happened FOUR YEARS AGO) and i have NEVER thought of it once until April ( incidentally after a big life event that stressed me out) SO i fought with this HORRIBLE feeling for about 4 months. I felt like a cheater, like i didn't deserve to be married, a liar, scum of the earth, debated asking for forgiveness by confessing. BUT i decided.... i cant do this to my husband, becuase what if i get past this and I know its OCD but once i plant that seed in HIS head HE will ALWAYS wonder if i actually did cheat on him. So i started practicing ERP, i got on antianxiety medication and started seeing an NOCD therapist. and i started saying " if it didn't matter then, it doesn't matter now". I am now recovered from this... i still don't know 100% that i didt cheat on my husband, but i am 99.99999% positive i didn't and that's good enough because you can't be certain about ANYTHING in life...
Long story short. your experience sounds exactly like mine. life is good- OCD T-bones you out of the blue- you wrestle with it and compulsively analyze it- you get relief, you think you solved it- OCD morphs and comes back around for another collision, and you are now at the point where you either keep doing compulsions, keep analyzing your memory(useless btw) and trying to solve the problem( compulsive) which MIGHT work, you MIGHT get relief again...until OCD comes around with something new.OR you accept its just OCD, you accept that you know you're self, you know you probably didn't do what you fear, and you run with it. And in time the acceptance will help your true self reemerge and the anxiety and fear will go away.