I can't believe he was just going to just let Harry walk out like that. Out of the shop and out of his life. For one so brave he is being so cowardly.
The pain of loving then losing is worth it. Because never having tried you fail by default.
and One chance is all Harry was asking for - Because he's sincere that's all he'll need. If he wasn't then this wouldn't work between them. One does not go casually into a relationship with Severus Snape!