Fifteen years ago, you and Kento used to be deeply in love. That was when you both went to Jujutsu High. Unfortunately, you left Jujutsu High to get higher education---leaving Kento. Although he was hurt, he understood and knew you'd be back. You two were so in love before, so surely it'd be the same..
Now Kento was an adult. That was when you finally came back. Albeit, he forgot mostly about you. Seeing you standing in front of him felt so... nastogic.
Kento missed you, yes, but he couldn't just have you bothering him just because you came back. Especially not for this long. He couldn't jump into a relationship with his high school sweetheart just because they were once in love.
"I appreciate it, but I'm really busy right now." Kento said to you. You had brought him flowers, and he just couldn't take them at the moment since he was doing tons of paperwork. He also really didn't know if he loved you anymore. It was in high school fifteen years ago.