Tell him to leave immediately and come back in a couple of days when I'm not feeling so homicidal, get his stuff, then leave for good. When it happened to me before, I simply left. It was his house and I didn't want it. Now this is my house, and no one is going to take away my home again through their selfishness.
That said, despite the pain caused by cheating in my past, I dearly love my husband, and as much as I've always seen cheating as a definite deal killer I honestly don't know if I could stick to my guns if it were him. Luckily, he loves me too, and has been cheated on before, and I trust that he would never inflict the kind of pain he had to live through on me.