I don't know of any poem or website that would help you say what you want, but you might just try sending him a card letting him know that you love him and when he is able to make good choices and respect you, you will be there for him. He may not want to hear it, but atleast you know you've said it.
It's called detatching with love. When he's making poor choices, you can walk away, when he's making good choices, you can be there for him.
Many of us have had to do this and believe me, it will be good for both of you.
If he has a drug problem, you may want to get yourself to an alanon parent meeting. Everyone in the room will have been, or currently is at the point you are now.
Welcome to this site. It is a life saver for many of us.
