Have you ever stopped to think of what dumbledore really saw in the mirror? Not socks. Maybe not even his sister alive. My theory is that what he saw was getting older, and watching a son grow up to be just like Harry. I mean think about it. All he does is try to protect harry. And you might say its because he knows harry could stop voldemort. But I think its more than that. He could have easily trained harry one on one in advanced magic a lot sooner. Or revealed more than hrme did. But he insisted on protecting him. Emotionally, mentally, and physically. Just like how a father might protect his son.
He sees Harry as a son.
Boom. Hammer dropped