R.,
I am sorry for some of the awful responses you got, jeezz Liz!!! Nice how some are so quick to be SO judgmental!! R., I agree with the the idea of depression. I have been there many times and it brings out a person in you that you never knew existed. The person that comes out when you can barley deal with life can be very ugly, but is only temporary with help.
Although your son's behavior is not acceptable he must be feeling so awful inside. Lost his marriage, lives with his parents and has two girls that he has to be a mom and dad to. That is alot for one person! My heart goes out to all of you.
I agree with pursuing the treatment for depression. Medication is helpful but to get to the root of the problem he probably needs to talk with a professional and might find great comfort in getting all his feelings sorted out and learning how to get back into life and take care of himself and his girls.
You DID NOT raise a bum!! (what a awful thing to say!!!) Your son is having a hard time and needs support but that does not mean enabling him. You will need to be strong through this too. Sit him down draw some lines and tell him that these things are not acceptable if he is going to be living in your home. The first step to helping yourself is VERY hard but once the step is taken each step gets easier. He probably feels very alone right now and very hopeless. Love and comfort from his mother might be the thing that pulls him out and walks him towards helping himself. Holding his hand does not mean doing it all for him.
Good Luck R., and Merry Christmas!!