And this past week, I got something to compare it to: He told me that he put boundaries up on a close friendship that he felt was codependent and that he was giving far too much to, to the point of it being a bizarre sort of emotional affair. This sounds very much like what you are describing here. He did just exactly what you are describing. He felt he was being used by and enabling this other person's emotional dependency.
(And the other person was surprised and hurt, but my friend felt he had to do it to survive and because it was morally unhealthy and wrong for him to keep going with things as they had been.) So thank you for explaining this. It makes a lot of sense in this other relationship that I just witnessed with him.
But the other relationship was not that way; I very much got the impression (having talked to him a number of times about it) that he felt betrayed because this original person let him down. He believed in him and had told him the right things to do, and the other person had given him lip service, then quietly proceeded with their plans to leave. (Actually, I think the ESFP was inspired each time my friend talked to him, to the point of WANTING to try harder; but he had no discipline whatsoever to persist when my friend was not around and the empty longings overwhelmed him.)