One way of looking at it is that if you were friends with T, the relationship would likely be LESS close. In other words, with a friendship you would likely feel restricted in what you could say to him, due to social convention and also not wanting to be a burden. (If he's married for instance, that would probably put limits on the amount of emotional intimacy you could have with him in the "real world")

It may be a situation of "The grass is greener on the other side". If you were his friend and not his client you might be really wishing you could talk to him on a deeper level - like you can in therapy.