Would you stay with someone who as cheated on you?

I am talking about if they are sound and mind not on drugs. I know a friend of mind her husband cheated but he was on drugs and doesn't remember any of it. How she found out was a message on his phone. For me, I would have to talk to my husband about what he did and go to rehab and be a trail base. I am sure my friend is devasted but after 20 years of marriage she really needs to think why he got into this mess.maybe he is depressed about getting old and the drugs made him feel better. All I know is I just there for her.