I don't think Toshiro will ever forgive himself even though Momo will definitely forgive him . Toshiro will never be able to get over the fact that he had hurt Momo with his own hands even though however long it had passed .
I dont think so much,he could never forget about Kusaka in the movie bleach 2 for years until he actually did the right thing.Well,he knows he did the wrong thing to Momo,even on accident,and he'll never forgive himself,unless he can fix it somehow.....
I think he would not forgive himself. For that reason that he has hurt a childhood friend. I somehow think he would wish to stab himself instead because he PROMISED TO PROTECT Hinamori which is why he would rather lose the position of a captain to defeat Aizen because of the state he left Hinamori at the Soul Society Arc. Which means that even if he KNOWS that Hinamori is fine and forgave him, he would assume that he isn't forgiven because it would be a shame for him to be forgiven when he thinks what he did is wrong. :-(