I Am Picking Up A Caviler King This Weekend. He

I am picking up a Caviler king this weekend. He was a rescue dog and has been returned to the human society several times from people who adopted him and cannot keep him for one reason or another. My friend now has him for the past four months and hasn't seen any progress in him. He will go outside only when leased and forced a little. As soon as he gets into the house he runs right up to her bed and wont leave there . She brought the dog here for a weekend end and the first thing he did was sought out a bed which was mine and retreated there. You never see the dogs tail wagging or any attempts to socialize with you. So she got another dog for a companion hoping that would help but it hasn't. This is why I am going to pick him up a see what I can do to help this Caviler King. My feelings are he is majorly depressed and im not sure where to start with depression. He has been checked over by her vet and he is health and was put on Prozac but he was like a puddle of water when he was on that. Any help or ideas would be gratefully taken.
Rick