I don't have intrusive thoughts so I can't offer a lot of insight but I do think these sound the way I would think that aspect of ocd would.

I'm sorry you are having such a difficult time. Unfortunately infidelity does exist but I think that these stories are exaggerations of reality. Distortions are common with anxiety and ocd is a form of anxiety so I think your brain could be distorting this.

Now out of my own curiosity I wonder where this come from and why it's this that is being distorted. Again I don't really know how obsessions work and I don't have any type of qualifications but I wonder. It seems that all of these thoughts point to a anxiety regarding women.

My phone won't open your profile so I'm not sure if your a girl or boy.
But if your a girl perhaps you lack trust in yourself. Do you worry that you won't be able to stay in a committed relationship
If your a boy or the first idea doesn't seem right, maybe you have seen some reason not to trust a woman in your life. I don't know, you don't have to answer here, I don't even know if ocd has the same way of developing as say my anxiety.

I just wanted you to know you've been heard. Is there anyone you feel comfortable in real life talking to? Your doctor? A counsellor/therapist?