Sasshi ga Yosugiru Ono-senpai

Yuzuki, a socially awkward college student who's used to a solitary life, is thrown into turmoil when the popular and outgoing Ono-senpai suddenly takes an interest in him! With his first confession, his first deep kiss, and his nerves in overdrive, Yuzuki finds his butt getting prepared before he’s even mentally ready for what's coming next. A whirlwind of emotions has this love-struck novice in overdrive—and now, nothing can stop him!

(Source: Libre, translated)

Note: Includes two extra chapters.