Been there done that! I agree huge mistake. But we are human.
I did a similar thing but only via email, asking him to tell me the truth about OW. This happened late at night. In the morning I sent him an email saying it was a mistake to send this to him, I don't want to know, what's done is done, nothing can change the past - told him not to contact me ever again and wished him true sobriety and happiness.
So far no contact and I've gone to extremes to block all email and phones from him. It's working and every day it gets easier, I actually go all day now without thinking about him and the 24 years we were together.
Don't beat yourself up and remember baby steps - K.