Someone once told me alcohol is like having an affair with a 'sour grape'. Don't follow him. No you're not wrong in saying no drinking. But is he really going to listen? He knows the boundaries, and you still suspect he's drinking, I can tell right away when mine has had even one drink.
Your intuition is probably right, I think if he was coming home instead of staying out he would probably stick to the boundaries. Do his friends know about the boundaries you to have agreed on?