Dazai loves being near to you at work just as much as he enjoys being with you in private. So, he takes every opportunity to be with you, whether it's holding your hand, twirling a strand of your hair in his hand while you work on reports, subtly leaning his head against your shoulder, and many more, enjoying your blushes and squeaks about PDA. Dazai loves you too much to keep your relationship a secret. You were his and he was yours, and he wanted all to know. He wanted to be caught with you.