Hi I can understand your problem very well since i was in similar situation as your guy. I will share what my boyfriend did to help me come out of it.
Before all that if you leave him he will become worse , you should at least help him as a friend if not as lover.
You should talk and express that you are not her and that the situation is nowhere similar to what had happened to him in the past.
He definitely needs lone time to think and come out of his past and realize that his acts are ruining the present.
each and every moment. Leave him alone for sometime and give him time to recover and if he still needs you he will come back for you
Meanwhile he can share his views with a psychiatrist or follow meditation to find inner peace. you can help him with that.