Not convinced that there is any value in telling a therapist this stuff. I personally have absolutely no intention of letting mine know that I surf her husband's profile to see if he has put any public pictures up of vacations or whatever, or that I know names of family members, or that I know which photographer they use for family photos. I want that information to stay accessible to me so I won't give her the head-start of knowing. And hope that none of her other clients are as snoopy as me and decide to tell her and she ends up shutting that operation down. Man, I'd be pissed.

The obvious detriment here is that it sounds like you're miserable holding what you perceive as this big egregious secret that will be responsible for the end of your therapeutic relationship? You're not guilty of doing anything except having curiosity and whoever says they haven't done any facebook stalking is either lying or selling something.

If it's the feelings of inadequacy that need addressing, maybe thats something that can be worked on with your second therapist. If it's the above mentioned misery of knowing something he doesn't know you know, then I guess the only closure you'll get from that is letting him know, or freeing yourself of some of the guilt with the knowledge that it's normal to want to know about the people in your life.