You had helped him. With SO MUCH. Just to find a cure for his sister Anne. And after everything, he’s so ungrateful for you refusing one more thing because you’re trying to keep him safe.
So after facing the Deathly Hallows. Even Death itself. He was still upset. He accused you of not wanting to help Anne. He said you didn’t care. Yeah right!
You didn’t care? He had no idea all the things you had to do to keep him out of trouble and to complete tasks that were impossible for everyone else, considering you were the only one who was able to see it or use it.
So as you fought, saying he didnt understand because he wasn’t listening to you, he shouted at you. “Why would I listen to someone so ignorant?!”
That hurt. It struck your heart worse than when he casted the Cruciatus Curse on you. And you didn’t think that was possible. It shattered you.
So you ran out. When he realized what he had said and how he had hurt you, he ran after you, trying to catch up with you and apologize, pleading for you to stop.
You opened your nab-sack and out came your dear Hippogriff friend, Highwing. You jumped onto her back and kicked for her to take off. As he saw you rise into the sky, he reached out in a desperate attempt to get to you before he slowed his run.
He was too late to catch up to you.