I SO totally do this too! So glad to know that I'm not the only one. I just get SO excited for that couple and then start thinking about how great my wedding day is going to be, which usually in turns makes it worse.
I have even done this while driving in the car and listening to the radio. There is one song by Phil Vassar called, "Love is a Beautiful Thing" that just opens the gates. My DF looks at me like I'm insane, and then he giggles at me. Oh well, all in part of being a girl, I guess.