Baito Saki no Ikuta-kun

Seeking a peaceful part-time job, Komae starts working at a coffee shop where he encounters Ikuta, a senior with a lazy demeanor. Despite this terrible first impression, after making mistakes at work, Komae discovers a new side of Ikuta, and before long, they become drinking buddies. But fueled by alcohol, Ikuta steals Komae's first kiss and takes his virginity without resistance... Komae wants to put a clear name to their relationship, but fears that doing so would sever his connection with Ikuta, leaving him with lingering uncertainty. Moreover, hearing stories of Ikuta having made advances on other new hires in the past, and stumbling upon him with another sex friend only intensifies his unease...

(Source: GOT Corporation, translated)

Note: Includes one extra chapter.