I'm giving up.
I don't think T is a horrible person. But I do think T has been behaving poorly, especially in regards to the many, many friends who've done T favors in the past. There's a very long list, going back at least to high school and continual overnight stays at friends' houses with indulgent parents.
My intention was to pick two obvious people to thank for recent favors, have T write a couple of lines to say "thank you" and then work backwards with other people who've been kind to T in the past. Verbal gratitude is all that T's given back so far, and not necessarily with an eye to the magnitude of what they've done for T. At the very least, the overdue "bread and butter" letters would get sent. (See also the 8th, 9th, and 10th steps of the 12-Step Programs.)
This isn't going to happen. The tantrums and justifications and misrepresentations to T's allies are just too much -- there are strangers and mutual friends who think I'm a terrible force in T's life. And some of them I care more about than T.
There's a long list of people who've done favors before and have stopped. They've disengaged. When T posts "tell me I'm a nice person," the newer friends chime in but most of the older ones are silent.
There are two futures divergent that I see. Either T gets proper psychiatric help, gets the correct combination of meds to help the brain function better, and generally starts making a better life. Which includes actual acts of loving kindness to other people, and not just constant empty declarations of love. Or T will end up a homeless wino living in a cardboard box. Or both -- it may take hitting bottom for T to realize what has to happen next.