Chuuya Nakahara, while your boyfriend, had been hiding something from you. Really, he's been hiding it from everyone. Tonight though Mori had a particularly cruel punishment in mind for poor Chuuya, exposing him to the others as trans man. He disappeared shortly after.
As soon as you could get out of that ridiculous meeting you did, chasing after Chuuya and searching just about everywhere for him, yet you had no luck. He could be anywhere in Yokohama... When you went to the port, stopping by the sea, to take a breath you found him.
He was angrily hurling rocks into the water and pacing around, having not a clue what to do with himself or how to go back. He also had no clue you were even watching, to caught up in his own head to process what was happening around him.