I can say 100% that if I was in this situation I would say no to him living with you.
BUT.....put the shoe on the other foot. In 9 years if your son was in the same position would you want to do anything you could if you thought it would help him? Would you want your DH to support you in whatever decision you make.
I understand where youre coming from, but he just wants to desperately save his son. Even if he cant save him. He wants to try. And he wants someone to support him.

I'm not saying you should let him stay with you by any means. I'm just playing devils advocate here and trying to understand how your husband feels.

The day Druggie would be moving back into my house would be the day HELL FREEZES OVER, especially with 2 young kids in the house.
Absolutely NOT. Why doesn't hubby and druggie get an apartment together? That way, Hubby can continue to enable him, while Druggie continues to take advantage of his guilt ridden dad.

Dysfunction goes around and around. Time to jump off that train. 5th rehab ? Sorry son, you are on your own !

Wow. I was actually your SS. I had the drug problem. And my father always tried to save me. And my step mom despised me being there and hated all the chaos I caused. Now that I have my own SD it's hard to believe how she put up with that for so long. . 3 years or so from someone who isn't even her own child. I got a say that if it wasn't for my dad and my step Mom allowing me to go back everytine I would be dead today. No doubt. They saved me and gave me a safe haven if it wasn't for them I would of been on the street. I also went to 3 rehabs only to go back hone and fail. My step mother always let me back though. I think cuz my dad insisted. Today I am sober and I thank my step mom for what she did for me. It put her at a lot of stress and chaos and sadness just to deal with me there but she did it. Probably because she loves me dad. Regardkessb to why I am thankful. I would say that if your SO wants to help ur SS you should maybe stand by him but set strict rules. And the number one is that if he cones home high or if there is paraphernalia found in the hone he is out that day. He has one more chance to do right and see if he takes that and runs with it. If he falls back into the same old trip u will have to think of step two but try to think positive. Ur SS doesn't want to be like this if he has gone to rehabs like that. He knows he needs to change. It's harder than anyone can imagine to get off heroin. good luck . To u and SS

How many times has DH said that this was the "last chance" to save his son?
Hell NO! Your kids are put in danger if he decides to go back on drugs. Not only can someone come after him, but if your kids see "candy," (ie drugs) they could overdose.
Your DH is enabling this behavior and unless SS hits bottom, he will never get why he needs to be sober. Hitting bottom may be that he will be homeless and go hungry for a few days, but you can not keeping taking him in. He knows that after a 6th, 7th, 8th time he can beg for forgiveness and come back to your house

When my SS left rehab, the counselors there advised him NOT to move in with family. He needed to be responsible for himself, be an adult, find his own way. Part of SS's issue is that too many people did too many things for him, and he didn't learn how to be an adult. This is a familiar story to many here. SS melted down and self-medicated instead, along with all the lies and stealing that go along with it. (BTW, he's clean for 3 or 4 years now and we're very very proud of him.)

He didn't move in with us, but moved to a nearby town to continue college (that lasted a couple of semesters, but he's never finished). DH helped him with rent, gave him a car, all those enabling and codependent things that DH couldn't see was part of the problem all along. He was, in his mind, helping. Thankfully DH finally backed off when SS TOLD him to. Yes, DH, YOU were in fact part of the problem. Talk about carrying around guilt, which he still does, and he struggles against his co-dependent disney dad enabling tendencies every day. Not always successfully either. But SS is making small strides toward and independent life.

OK you've done way more than expected of you by any reasonable person which doesn't include your husband. Tell him that if he insists you wish a separation immediately. Really - isn't it that or your sanity? I know you can't afford a great place without him just do the best you can which is what you'd be doing if you had never met him.

This boy will quit drugs when he's dead although statistically he has a chance and some do. All abusers like this quit, one way or another, by about age forty. But until he does you've got to make a clear point to your husband which I doubt he will take.