I agree with all that everyone here has contributed. That said, I think that I still need to look at this person as an individual. Will now address the rest to Deuce.
Deuce,
I think you and your H have really good hearts, and big hearts. Yes, for me it worked out for me in my case. I also didn't have this one "adopted son", I had many. For some reason my son (real son) just attracted many of his friends to our house. They were all troubled youths. My son was not, but in actuality he was. My son, later on in life, at age 22 told me that he knew my ex was abusive, but he then compared his life to his friends lifes.
Many of his friends stayed over, and I treated each and everyone of them with respect.
I fed them, I loved them, and I listened to them. I knew they were young, and back then I really had no boundaries. My only boundary was, if you come here at night, you are staying here. I knew they drank, and I knew some were doing drugs, I just wanted them safe.
So, I was probably wrong to actually know that they were drinking and doing drugs, but at that time that was OK. I knew they weren't driving, I knew they wouldn't be in an accident and die, or kill someone, while driving.
I was OK with this, don't know how I would be about this today.
But they talked to me, they felt the respect that I had for each of them. I know most turned out OK. Lost touch with some of them. But they do know that I loved each and every one of them.
And yes, listen to all the other advice given. It's very good advice and very accurate.
I can't judge this young man that is staying with you. I don't know him, and also, I can't judge another person. I always like to see the "good" in people.
My "adopted son" once tried to pull something in my house. My son told him, you do that you are out of here. Never had a problem after that. He wanted the safety, the security net, and we gave that to him.
Now just know that I am talking about teenagers. Abused teenagers.
Also know that I am a recovering alcoholic. My "sons" and I will say at least 10, didn't know what love and respect was. And there was that one that always stuck around, and I really don't know where I am going from here.
I know that I made a difference to at least one. I never wanted anything for it, never gave it a thought. Saw him last year, and he thanked me, and I didn't know why. He told me that because I believed in him, and that I saw him as a person, that I respected him, that he needed to prove that I was right about him.
He told me that when he dropped out of high school, there was just fighting at home, and that when he told me about this, he told me that I talked to him, told me that he remembered that I said, I should have no say in this, I am not your mother, but he continued to talk, told me when we were talking that it's ok to talk to him like a mother, said that no one talks to him that way. Told me that I was the only one that thought he might someday succeed.
So, I say yes, give the kid a chance. If he breaks or runs all over your boundaries, then yes, tell him to leave, then change the locks, and get a security system.