Stability for co parent with addiction

After being divorced 11 years, my childs father and my ex husband finds himself again divorcing his second wife.  He is addicted to crack cocaine and has been for many yrs.  Thank god he only uses about 1-2 times per year.  I would say I feel good about his recovery compared to when we were together and he used every 90 days.  Our child has special needs and I do not want to see him unstable as I fear relapse and possibly disappearance which would greatly damage the father son realtionship.  I have no romantic interest in him myself and I have been in recovery for many years from depression and ptsd.  I feel strong enough to give him safe harbor in our home for the summer, in order for him to save money and relocate in the same city with our son.  My only interest is our son although I will always care for his dad.  I think as long as we have boundaries and I provide support and encouragement to his father, both will able to move on to the next evolution of their life.  I accept that all of us on earth have our problems including myself and my ex husband.  I will not be used or harmed in anyway.  I will demonstrate care to him and our child.  IE love thy neighbor.  Does anyone have any ideas how I can make this a successful situation for all?  I made some space and provided comfortable living arrangements for when he arrives.  I will mind my own business and live and let live, as long as he respects our home. I have been mostly single the last 8 yrs so the whole dating issues doesn't really bother me.  I hope he will make good choices but I cant do anything for him.  I truly believe knowing that we care in a humane, christian way will help him continue on his self improvement.  This is a 90 day arrangement, small price to pay for a successful family.  Anyone please comment and tell me what things I am missing to make this more successful?