I am a wife of an addict so I cannot entirely relate. But I am a mother of a beautiful son, if my son was using- I would want to do everything in my power to save him. I understand your desire to do so. If you are going to bring him back into your home, then I would suggest to definitely set boundries, and never forget that he is an addict. And only let him stay if he is actively seeking help for his addiction. Don't be ashamed for wanting to help.
My thoughts and prayers are with you and your whole family.