[ have a friend whose wife found he has a mistress and kicked him out of the bed last night and probably the house soon...Does he have the right to stay in the house if he decides to file for divorce from her?

Depends on the state, in some states she can change the locks on him.

And I doubt that he has to worry about filing for divorce I am sure the wife will do it for him.

If he was cheating and was caught, he needs to move out for a while, try to get marriage counseling with his wife and make it work.

He doesn't have to leave.

It is much his property as his wife's.

Hi,
If the wife sees a lawyer, has Separation Papers drawn up, then he will have to move out. It's up to her.
Since he is the one who initiated the problems, I am almost certain the lawyer will have the Court tell him to leave. Later, if they divorce, half the value of the house and property will be his, unless some other considerations are in order.

Im not sure you can make someone leave there place of residence. But put it this way if I was the wife id leave if he wouldn't