Why would he do this?
Say you're friends with this guy, and you were at a party with a lot of other friends. You were talking with one of your other friends about something that happened to you a few years ago when you notice them look over your shoulder, and you turn around to find your guy friend standing behind you. But you had no idea he was standing there or how long he had been there. Why would he do this? Is it a way to learn more about me without me knowing?