I believe I am experiencing real event OCD and I am literally thinking about the event 100% of the time, while awake and asleep. I'm not sure that it is an "intrusive thought" so much as an ever-present thought. This makes me feel like it's not really OCD but actually well-deserved guilt. I'm curious to know more about how ERP could help with a thought if its ever-present, rather than popping up.

“Intrusive” applies to any thought you’re not bringing up on purpose. It might be something that pops up from time to time, or it might feel more constant. In OCD, certain thoughts provoke distress and anxiety and we do compulsions to try to make them go away. It sounds to me like you are engaging with the thought compulsively to try to figure it out and lessen your anxiety. The response prevention for this would be to accept/agree with the thought. Instead of compulsing, choose a lean-in like “maybe that did happen, maybe it’s my fault” (or if that feels too distressing, simply “ok” or “maybe.”) This won’t make the thought go away, so you might spend quite a few days just saying “ok,” “sure,” “whatever you say” to it in your head, and it might feel very uncomfortable. Over time, though, the thought will lose its power over you and fade into the background. In terms of exposure, you might write out a script of what you feared happened and your feared consequences. “I might never know that I made a mistake,” “not feeling guilty could be the wrong thing to do,” etc. Read it and practice agreeing. If this is too anxiety-provoking, a therapist can help you figure out smaller exposures that work up to it. As for the “what if this isn’t OCD,” treat it like any other obsession. No one can actually look inside of our brains and determine with 100% certainty that we have OCD. Work on accepting that this might not be OCD and that you can’t know for sure. I hope that helps. Best of luck!