Thanks for the further information.
Your fiance son has two issues;
1) Psychological; depression and occasionally getting violent.
2) Behavioral issues; drinking beer, smoking (cigarettes and/or drugs).
Both of these are significant and need urgent attention. The reason is future worsening, which is known in all of these. The prognosis is poor if not treated promptly, continuously and effectively. These are finance draining, time consuming and seriously compromise quality of life. I am sure, your fiance would be understanding them as he has admitted him to Rehab for many times. But there is rebound and resurfacing of the problems, so surely these have not been handled completely and were managed inadequately.
You should talk to your fiance. I am sure you must have done that, earlier too. But a newer perspective have to be given to him that he has to choose a life with his son and his problems or a quality life with you. I see that talking and firmly assisting him chalking out executing a treatment plan for his son; could be the best solution. You may consider taking firm decision on your fiance's behalf, for a long term treatment measures of his son.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.
Thanks for using Just Answer.