struggling bad after diagnosis, need advice!

So yesterday my therapist officially told me that what I'm dealing with is ROCD, although I already had my suspicions. It was a relief and my partner has been supportive so far, but I'm stuck thinking that maybe I'm faking it, and that the false memory and intrusive thought of "what if I cheated on him and I don't remember?" is actually true, and I'm just in denial. My "proof" for this is that I did do something wrong once and hid it, but in that case I had a very clear memory and proof. Now, what I have is verbal proof for considering my intrusive thought as what it is- a lie. But the feeling that I've cheated (which I haven't) doesn't leave and I feel sick to my stomach, unable to enjoy my relationship... Has anyone dealt with this?