Shuugakuryokou de Nakayokunai Group ni Hairimashita

Hioki somehow gets invited to join a group of four good-looking guys for a school trip. Though initially riddled with anxiety, it turned out to be surprisingly fun, largely thanks to Watarai, who goes out of his way to look after him. Just as Hioki began to open his heart to Watarai, what emerged was not simple kindness—but obsession.

(Source: Starts Publishing, translated)