Hi Paula. I know I'm just the ex of an addict and the mother of a 4 year old boy who has a father for an addict. So I don't have the exact same situation you have. But every son has a mother and my ex used and devastated his mother (and the rest of his family) with his drug addiction.
He's been smoking crack and lying about it for 20 years. He's in and out of prison. He still breaks his mothers heart on a regular basis.
I just think if she would have drawn firm boundaries early on, things might have turned out better for her - as a young adult he wouldn't have lived at home for free, using drugs, stealing from her, stealing from everyone around him. She could have said NO. But she didn't.
She ended up losing her house because of it. Everything she had went into storage. Then she lost the storage too - because he was supposed to be making the payments and he never did. And I really blame her son for that. But she never stopped thinking "it was only pot" and she never believed that her son could do those horrible deceiptful things to her - even when the evidence and the foreclosure notice was staring her in the face.
I really encourage you to examine yourself and your personal values and then draw boundaries based on those values. Not boundaries that are especially designed for your son but boundaries for yourself about what is ok in your life.
I hate drugs. I do not allow drugs around me or my little boy or my house. I refuse to be around them. Therefore, I don't care who you are - I don't care if you are Jesus, Mary or Joseph. You will not be allowed anywhere near my house if I suspect you are using drugs. And if you come around and don't leave when asked, I will call the police on you to be escorted off my property.
That boundary is for everyone - not just my ex. I mean, if I'm not serious about it for everyone. Why say it at all.
The sad thing is that I've actually had to use it. I've had to follow through on the consequences. Addicts WILL push your boundaries. That's just what they do. That's what THEY ALL do.