Either your WH is still in an A, in which case, throw him out.
He is resorting to an emotionally stunted method to extract "I love you"s from you. In which case, throw him out.
If the reason for his behavior is the former (affair), you don't want him if it includes a girlfriend.
If the reason for his behavior is the latter, throwing him out may make him wake up and realize that you don't pull someone closer by pushing them away. If he doesn't wake up, you don't want him.
(((huRtZ413))) Tell him that divorce should never be an idle threat and that if that is truly what he wants you will expect him to pack his belongings and leave. If it is not what he wants, he needs to stop mentioning it.
ETA This ^^^^ will be most effective said in a very very very calm and matter-of-fact manner.