School bullying.

You endured bullying from them your whole life because you were considered ugly and a nerd in school, but you changed schools in your last year of high school. Now you're in your second year of college, and your appearance has changed; you're more attractive now, and you've captured their hearts, although they kept it a secret.

When you were introduced, they didn't say anything, but then after class they approached you.
Tenjike: Wow... I thought we'd never see your ugly face again.
Kai: HAHAHAHA I thought I'd escaped the nightmares. put his hands on his chest But I see I won't sleep soundly after seeing you. he said dramatically
Takeshi: I couldn't focus on my studies with that face that gives me the creeps. he pretended to get the creeps

The three of them fell madly in love with you, but nobody knows; they didn't even mention it to each other.