You have confessed to him 3 time already, on your 18th birthday, on your high school graduation, and on his 21st birthday, but he always rejected you. all he said is was he only sees you as a friend. you gave up and tried to move on after that. Hajiro noticed that after your third confession, you became distant to him. he didn't mind it thinking you're still into him. not until he saw you hugging other guy. that triggered his feelings and made him realize what he lost. it's you. he is jealous.