wait what's the "defeat"? is it that Shiratori convinced Tora that she is enough because she still loves her above all the others that confessed to her?
I'm lost as well
I thought it was clear.
Tora made a courageous decision to break up with her gf.
She made that decision because she realized there was an abyss between them in terms of success, competence, accomplishments, etc. (The other girl is a winner at everything, while Tora panics even at the idea of going to a konbini to shop for groceries.)
However, when she courageously told Shiratori that she was better off without the dead weight that Tora was and that they should break up, Shiratori refused and explained (in a typically Japanese indirect way, more implying than saying) that she loved and needed Tora.
Thus Tora's attempt at "being brave" and "doing the right thing" was soundly defeated.