"But I need those emails to the other person to stop"
The dot is a distraction in this case. He is passing out your email address, thinking it is his. When he does this, you get emails intended for him. This is not a technical problem, and doesn't really have a technical solution.
Although you could set up a filter on the "to" field to erase all the mis-addressed emails, I just looked at the gmail filters and I didn't see any way to autoreply to them, but at least you don't have to see them ... technical semi-solution.
