I've written about this before, but this thread of a positive experience of friendship post-therapy seems the right place to mention it again.

I still keep in touch with my first therapist from 30 years ago. We talk or email several times a year, and if we are in each others' vicinity we might meet for lunch. We aren't best buds; we are more like old friends who keep track of each other.

It has worked because a) there never, ever was any possibility he would be my therapist again b) we live a good distance from each other which provides a safe bubble for each other c) we don't discuss topics that are therapy fodder d) I don't pretend that our relationship is any more than it really is, and e) i had no attachment or transference issues with him to over-complicate matters.

I do believe it can happen if the therapist and client both have very healthy boundaries and very realistic expectations, but that in itself is the big question. My guess is that most therapists don't enter into these kinds post-therapy relationships because they see that those conditions just aren't strong in most cases. They have to to have some common sense about such things, (and there is always the primary factor of whether they would pursue any kind of relationship with a client at all if it were not for the therapy relationship).