It's like a living, breathing entity inside him, the anger he feels.
He first notices its existence in third year, when he fears that Hermione's interference has lost him the only chance he might have to ride on a Firebolt. He doesn't realize what it is that compels him to shun her – to convince Harry to shun her.
The anger grows steadily.
When it looks like Scabbers has been eaten by Crookshanks, it reappears. He loses his temper with Hermione once again. It's all her fault, the anger whispers to him insidiously. She should have kept an eye on that beast of hers. She knew it was after Scabbers.
It doesn't matter that he never cared about his rat. All he knows – all he cares about – is that he has been wronged.
When he learns that it wasn't her fault – it wasn't Crookshanks' fault – it doesn't matter. He is angry at Pettigrew – he hates Pettigrew – but the anger at Hermione is still there.
Because he could have been right, and that's all that matters.
The anger stops him from him apologizing. Stops him from admitting he was wrong.
He doesn't think that it's a problem. Why would it be? He was right, wasn't he?
He only realizes how wrong he is when he betrays Harry. Because he was wrong, and Harry could have been killed thinking that his best friend didn't give a damn about his life. He could have died thinking Ron valued fame and money more than him.
Sometimes, in dreams, he remembers Hermione telling Harry that there are more important things than books and cleverness. It used to shock him that Hermione thought that way. Now, he thinks he understands.
The anger is still a living entity inside him, but now he knows about it. Now, he understands it.
He teaches himself to control it. He isn't going to let the anger take over again, isn't going to let it control him again.
Because the anger might forever be a part of him, but that is all it will ever be. Only a part, never all. Never him.
For:
The If You Dare Challenge, Prompt 127. Several Deep Breaths
The Snakes and Ladders Challenge
All Canon Bootcamp, Prompt 16. "But I hate it!"
50 Different Friendships Or More Challenge, Prompt 3. Betray
Magical Objects Competition, Howler
Weasley-Prewitt-Potter Challenge, Ron Weasley
Gemstone Competition, Garnets