Image of partner with someone else

I’m wondering if anyone else is affected by details of their partner being with someone else. When my partner and I agree to try being open, I didn’t realize that I was asking for it to try to “prove” I still had desire and ability, but when she was actually with someone else, I lost my shit and felt the crushing weight of all that insecurity I had been trying to run from. I pressed her for details and although they didn’t have sex, they did get each other off orally and this guy was apparently big enough that he “gave her a warning” beforehand and she admitted her jaw was sore, etc.

We’ve continued to see each other and are back to being exclusive but many of the times I see her, and even when I’m on my own, I can’t shake this specific image of her with this person and contrasting that to my own anxiety, size, worry about performance, etc. Its gone so far that at points I think my brain wants to actually eroticize imagining them together (almost like cuck fanttasy territory) rather than feel the pain of jealousy and doubt, which is horrible in its own way.

I was wondering if anyone else has struggled with this specific version of the “inner critic” and what has helped. My partner says she prefers me in every way but of course that’s really hard to feel when I don’t have love for or trust in myself.