But seems they often do get clients severely attached, in a way that is not found in normal relationships. And clearly it's not uncommon for clients to feel unable to function when faced with loss of the T, even if it's just a break imposed by a long vacation.

I think comparing this to outside relationships in terms of the potential for heartbreak and pain misses something fundamental, because of the nature of the relationship -- the idealized figure of the T, the parallels to parent-child, the fantasies of the perfect relationship, the emotional dependency, the disparity of need. I found it to be too close to institutionalized cruelty when it ruptured and when it ended.