Deathbed confession.

How do you know that your dads talking about the same woman from 30 years ago? He may be talking about someone he met at the nursing facility as that is so very common.
I think that you're making this bigger than it has to be, as you supposedly knew about the "other woman" 30 years ago and chose not to do anything about it, so choose now to just ignore what your dad says and let him die in peace with a clear conscience.

You don't have to allow him to divulge things: use distraction or redirection to change the subject. IMHO it's not worth spending any emotional energy over since it may turn out to be false or inaccurate. Recently, for several days in a row my Mom kept alluding to some "secret" she had and wanted to tell me. Eventually she told me that her in-home caregivers were drinking her booze. How do I know it's not true? Now whenever she can't find something she blames it on the caregivers (who have not been in her house for 2 months now) OR on me. Why would a caregive want to steal her plastic wrap. Or me. Now I don't let her go down that path because its tiresome and keeps her mind in a paranoid and negative place. Get out your phone and look up funny or sentimental videos on social media (like YouTube, IG, etc). Play him some music, show him pictures... anything to change the direction of the conversation.

It's up to you whether or not you want to spend time with him. Don't feel like you have to, if it will cause negative feelings.

I’m sorry you had to hear that and hope you can put it out of mind soon. It’s truly useless information that benefits no one and shouldn’t be voiced. I bet even dad didn’t feel better for sharing. Do what you need to move forward in peace

If I were to hear a deathbed confession, I wouldn't tell anyone. It would die with me. However, I'm sure I'd find it very interesting!

I don't know whether I should reveal this (my own secret!), but if a dying family member told me secrets, I'd be excited. I'd consider it to be a final opportunity to learn more about my family's past.
That said, I think it's okay to say to your father, "I don't want to hear secrets," and then suggest that he speak with a spiritual adviser (for example, a priest, a minister, or a rabbi).

My mom wanted me to find out if she had harmed/killed someone. She couldn't remember. She said with my research abilities I should be able to find out. She stopped talking about it and we moved on. That was over a year ago.

Its already too much, what's going on with your parents all these years. Then add in this deathbed confession and it throws it all way over the top. The selfishness of the elders never ends, it seems, and the burden for us gets heavier and heavier. This probably feels like the proverbial straw that broke the camel's back. I know it did when my mother did her little confession presentation. From that day forward, I never visited her alone again. I took DH with me as a buffer bc she was always better behaved in front of "outsiders".

That idea may work for you too with both of them. I hope so.

I'm sorry you've been put in this position and pray you find it easy to put it ALL out of your mind and find peace. You sure deserve it.

Just read a novel called Jenny Cooper Has a Secret. Be glad it's not that!! BTW the book was a hoot!! This situation,, but darker! Set in a NH, dementia.. THIS !!

Why are you so PO? All the stats say that a surprising proportion of adults have or have had real or imagined experiences outside marriage. Nothing shocking about that! Are you totally pure yourself? Or were you looking for a reason not “to call or visit again”?