Given this history, should I try R?
No 'should' here. Do you want to R? Do you want to live the rest of your life with her? If not, my reco is to D. If yes, my reco is to R, monitor key performance issues, and D if one or both of you stop doing the necessary work or decide to D.
Given that she loved him so deeply, will she ever be able to truly forget him?
IMO, the love is false. If it were true, she'd leave. Sometimes WSes leave for false love. But IMO, aps can't feel true love, because they live in a fantasy.
Most of the things in our marriage was good. How could she choose an affair for her own selfish excitement and ruin our marriage?
Beats me. Shirley Glass (look her up) wrote the As happen in good Ms when the WS has poor boundaries. That seems to fit your WS.
I am unable to accept that she risked and ignored marriage, children, family reputation, H pain/trauma, and enjoyed her affair for two years and now wants to come back and resume earlier married life.
If you want to R, try out R. If she wants R, she'll do the necessary work.
Does she deserve to have a happy married life after doing all this?
If you want a happy M with her, she has to have a happy M with you. If you don't want her, choose D. Then the question becomes moot to you.
Every day, I get triggered, especially by the AP’s message describing their intimate acts, her ChatGPT messages such as "We love each other" and "I liked meeting him," and the affectionate names they used to call each other.
Why didn’t I tell her to block his contact at the beginning, when she informed me that he was sending her messages?
Gently, why are you asking us a question to which only you know the answer. Have you notified om's W? She deserves to know, and you might throw a wrench into his works. His W deserves to know. Any satisfaction you feel for telling her is beside the point, but enjoyable nonetheless.
Why didn’t I check her phone earlier and discover the affair?
I read this as a tragic, understandable lament. There's no blame in trusting your W. That comes from love. Really, there was nothing else a loving H would have done. My reco is to mourn and forgive yourself.
AP once told my W, "Beautiful women are not available; we steal them from careless men." Was I careless, and did my carelessness contribute to the affair?
He's a prime asshole, a POS of a man. There's no punishment that would be appropriate for him. You know the answer to this question, but my bet is that your W didn't have the boundaries she needed. She was a lousy person; you did your job.
How can I stop thinking about these things?
Heal. Feel your pain. Figure out what you want, and do what you can to get it. D if you don't want your W or if she doesn't do the work of R.