I feel I can appreciate what you may mean about the 'begging.' It doesn't sound like you really want to torment him over the affair. It sounds like you may be baffled, by his just walking away, and not fighting to save the marriage and having all those talks, that many people would attempt to have.

For instance, a conversation could go like this:
H:I cheated, 8 years ago
W:Get out of my home, I don't want to be involved with a cheater
H:I'll leave, but will you please consider taking me back, if I go get some help?
W: I may consider taking you back, after a certain amount of time, or let's go through counseling, so I can see for myself if I do want you back.
H: I appreciate the consideration for a second change, I love my family and am so very sorry for making such a huge mistake.

He cheated 8 years ago. It was brought up, after 8 years. And when asked to leave, (my impression) "Yes, I get to leave now, see 'ya" (because I am considering someone else...type of thinking)

It truly seems bizarre, that he's not pleading for his marriage and presumably family?!