I think if his wife leaves videos of him on the public domain then it is obvious you and other clients are going to come across them. Unless you signed a contract with him saying you would not look at any thing about him on the internet, I do not actually think you have transgressed. Maybe the virtuous thing to do is to suggest he sets his wife's privacy settings higher and also really, you should not be a Facebook friend of your therapist's wife!!
Oh the anguish we go through as clients. Sending hugs