Its not his fault>Stain says that what defined All Might was his smile and his courage, not his power, and that this is the only version of All Might he can accept. He says that the current state is not the "end result of his efforts" at all, they are still the middle part of a process.
He says that the embers left by All Might have not been blown out by even the strongest of winds, and have been passed on to a group of people, who have turned them into a huge fire that continues to grow.
All Might begins to cry as he watches the lady. Stain then says that he is unable to recognize All Might in that person right now, but if he really is the true hero he so admires, he should use the information Stain obtained on Tartarus and kill him, putting an end to the Hero Killer. He throws a knife on the ground near All Might, containing a piece of paper with this information he talked about.
He finishes by saying that this is all for the sake of a more just society and All Might is still crying. The girl looks at the sky and realizes that the rain is stopping.
And he already got over it after this conversation.