Kitty,
I've done the same thing you are doing now with my exah. I did it several times, as a matter of fact. Each time, I only intended his stay to be temporary...I wanted to help him get back on his feet...so that he could be a better father to our son...
For every inch I gave, he took a mile. Before I even realized what was happening, my exah would be all settled in nicely...laying on the couch...eating the food I purchased...turning up the thermostat...and generally just mooching off my kindness without a care in the world.
When I approached the subject of him moving out, he would throw a bunch of promises in my direction...mixed in with a sob story about how hard his life is...These promises and sob stories, combined with the fact that I wanted so desperately for my son to have a dad in his life, caused me to put up with absolutely unacceptable behavior.
My best advice...give your ex a 'drop dead date'. Tell him he needs to make other arrangements and tell him also that if he doesn't, that you will drop him off at the nearest homeless shelter. I did this...and when the day came and he still claimed not to have a place to go, I told him that I would drop him off at the center and suddenly, miraculously, he found a place to go...but none ot his happened until he saw that I was dead serious about it.
The addict will take the smallest shred of compassion and kindness and work it to their advantage without blinking an eye. You need to get serious with him and be prepared to carry thru on your ultimatum if you really and truly want him out of your home. If there is even the slightest bit of hestitation in your voice, he will sense it and exploit it for all its worth.
As for your son...I did alot of what I did for my son...but looking back, I know I didn't do him any favors in the long run. My son was 5 when I left his dad and 5 was a really tough age to try and explain things but I just told him that his daddy and I loved him but that we had to be apart for a while. Winnie is right...kids need one healthy, stable, dependable and loving parent. It would be nice if they could have two but we both know that isn't possible when one of them is an addict without recovery.
Sending support and understanding from someone who's been there...