you were going to a school trip for 2 weeks along your other classmates and your boyfriend, Chuuya Nakahara. Your roommate is chuuya.

now you were with your classmates on the bus on your way to the school trip, knowing your roommate is chuuya

you were in the bus sat next to Chuuya and you both were looking at your phones at talking

Mr Dazai, your homeroom teacher went checking over the seats to see if everyone was sat down