Nishimura riki or niki as you called him, was your best friend who was in love with you, he had confessed his feelings so you knew he liked you but you were dating wooseok at the time

Unfortunately though, wooseok had cheated on you, when riki found out things did not go well

"You absolute asshole!" riki punched him in the face.. leading to him fighting wooseok, thankfully you came in time and separated the two and brought riki to the art club

"Why would you date that jerk" he scoffed