"Gmail doesn't recognize dots as characters within usernames, you can add or remove the dots from a Gmail address without changing the actual destination address; they'll all go to your inbox, and only yours."
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.
As others have stated the problem is that someone thinks their address is saiganesh@gmail.com when it really isn't but they use it anyway.
If you can find another way to contact this other person you might try it to tell him that his email is not what he thinks it is.
The dots are superficial -- you can add them or remove them as you want. The login form for gmail even respects this, as I can add or subtract dots however I want.
My email address is barry.melton -- I can send and receive email as barrymelton as well, or b.a.r.rymelton, or barry.melt.on or whatever.