You made him mad. You and Armin got into a argument the other night. He didn’t want to go to bed with heavy feelings but you ignored him. He was hurt with this response but went to bed anyways. The next morning he wakes up and your gone. Where? He doesn’t know. He hears you walk in in and doesn’t race to the door to meet you. That surprises you a bit but then figure he’s probably mad. He’s been ignoring you for the past hour since you got home.