I guess you would be distraught, but I happen to think that you seem to be taking a lot of unnecessary guilt upon yourself here. How much of this is your fault?? In my humble opinion. None. You are the one who has remained grounded here. Its unfortunately his own actions that have led to these consequences. If the pressure of being with you and wanting her is too much, then why couldn't he leave? If his life is that out of control, then he A) really needs more help than you can give him and B) needs to make his own choices about his life.
sorry if this seems harsh, but, my goodness dear. I hate to see you beating yourself up for the actions of another. Its not your fault, you know that. In essence, he is going to have to "man" up at some point and decide either he wants to be with you or make a way to be without you.
"Achieve success, but without vanity; Achieve success, but without aggression; Achieve success, but without gain; Achieve success, but without force." Lao Tzu