Oh God, I really worry about doing this as I frequently check the page of a close relative of my T. I'm super careful about avoiding the 'add friend' tab but even so it's very easily done, especially on smaller devices, so don't beat yourself up about it. I would probably react in a very similar way, plus be absolutely terrified about facing my T at our next session in case her relative happened to mention the request (which I suspect they would).

I don't have any idea how the technicalities work I'm afraid. I still worry about whether people can see if I have looked at their page and whether if facebook suggests you as a friend if you have looked at their page. I don't trust any of it. I wish I didn't look at the relative's page but it's hard not to.

I'm sure you won't be thrown out of therapy though! You won't be the first client to have done similar I feel sure, and you won't be the last. If you can contact him by text or email maybe drop him a line and apologise for the mistake so he can pass it onto the friend?