Irrational Guilt in 5 month relationship

So no one I ever spoke to has been through this . In every relationship I get into where I think the relationship has potential and will last , I seem to tell myself “what if you cheated on him” and then I’m in my head like “no you would remember “ and I’m like “but what if I don’t remember “ and I spiral down and lose myself and create situations in my head . I’ll bring my past into my future and make it seem like I cheated . I will go and find proof that I didn’t do it and if I can’t find proof I freak out and want to confess . Even tho I DID NOTHING WRONG . It’s awful and has taken a tole on me to the point where I had to get on meds . And the meds saved me . But I still feel these ways, but it doesn’t affect me going to work , or losing sleep ; and eating meals anymore . I never want to feel like a bad person

I had a life before I was with my partner, that involved having girlfriends and one night stands, etc. That's a lifetime of memories that I now feel guilty for having. Something as silly as watching a TV show with my girlfriend will make me think "I used to watch this show with an ex, is it ok to watch it with my current girlfriend?" and I will feel real guilt over it and need to seek her reassurance. There are other memories, about "intimate" times, that sometimes come into my head and I have urges to share them with my girlfriend to alleviate the guilt I feel for having the memory. Fundamentally, I feel guilty every time I have a memory of an ex, often regardless of the content. I feel like I shouldn't have thoughts of anyone else other than my current partner and it's wrong to have memories of exes. When I do, I feel guilty, ruminate, then have the uncontrollable urge to share the memories with her. She gets upset, I get upset, but also feel relief that I've shared. Does anyone have any similar experiences and/or tips around this sort of issue? Thanks.

I often feel like i did something wrong even tho i am positive i didn’t, my boyfriend and i have been together for like 6 months and i’ve been completely loyal to him the whole time but recently i’ve been feeling the need to confess that i cheated on him even tho i didn’t and there’s absolutely no proof that i did something even close, i don’t talk to other men and if i do my boyfriend has full access to my phone and it’s usually a friend or me asking a simple question but i still feel the need to confess even tho i’ve done nothing wrong🥲 someone please help it’s so confusing