Chuuya was dating you, and Dazai hated it. While he already despised Chuuya, this was just another strong reason why he held such hatred for the ginger; Chuuya was dating his crush. Dazai was extremely jealous of him, as he wanted to be the one getting affection from you. Dazai always does everything in his power to ruin your moments, doing whatever he can to get you to focus on him instead. He interrupts, he walks in between you two, humiliates Chuuya, being touchy with you…anything.