I always thought it would be a dealbreaker for me... until I was faced with it. On DDay I immediately offered R, which surprised the hell out of him.
He was remorseful and was doing all of the right things (NC the OW, offered to leave his job)... for about three days. Then he started getting defensive and cruel, calling it "honesty." I 180ed.
By week 3 post DDay, I figured out that he had taken the A underground. When I found out, he got verbally and emotionally abusive. Started saying he wanted me to get a sublet, etc.
I NCed him on the spot. I haven't spoken to him since.
... AND IT HAS BEEN HELL.
I wish to God he hadn't been so unremorseful and forced my hand. The hell of S/D and NCing the man I love and my bestfriend-- and facing that I'm never going to have the life I though I had again, the children I wanted, etc-- it's agony.
Another SIer told me it's like pulling yourself out from the brink of death. I think that's about right.
So I get it if you stayed. In fact, this shit is so hard, I don't know how people leave, short of a case like mine where I refused to be abused.