DON'T DO IT.
I commend and admire you for wanting to help your friend. I am sure he appreciates the gesture. Here's the thing: if living with his family has not given him the opportunity to start turning around his life, living with you won't do it either. Both of you will be better off if he does the following:
Consult with a credit counseling firm to plan how he can pay his debts, avoid incurring new ones, and learn how to manage his money. Greenpath Financial Wellness is one that offers both credit and housing counseling. They do not offer debt "settlement" nor do they offer sham consolidation loans. I've had friends and family members work with them and they were great.
Get a small studio apartment. He will only be there on weekends, so the small size won't matter.
Seek assistance for his drinking and spending habits. This does not have to be AA. It could be therapy, a discussion/support group, a sober meetup group or any of the myriad other ways to socialize and get help with kicking bad habits.
You can help him by being supportive, asking how he is doing, and being there for him when he falls down.