Hi Dime. I wouldn't tell your friend about this possible tell, unless it's so obvious that everyone spots. In which case it's probably not as much use to you. If it's a gem of a tell, then definetly keep it to yourself - it could come in very handy.
I wouldn't worry about him being taken advantage of either, since at other venues he'll most likely be playing with strangers, who won't have the same personal history as you've got with him.
One thing though - don't tell everyone at the table you have a tell on him. It's not nice and he won't thank you for it. Keep it to yourself and act upon it when the time is right.
Anyway, what's the tell?
