Koi wa Kataru ni, Ochiru Mono.

From Yuzu Scanlations:

“I’ve already loosened my ass up…”
College student Ise Natsume may look like an ikemen, but he’s just a silent person with a lifeless face. Even though he has only a few friends, let alone lovers, he falls in love with someone he just met. That person is Amano Haru, a classmate who’s cute, friendly, and expressive, the exact opposite of Natsume.
As he watches Haru from a distance like a stalker, his friend decides gives him a warning: “That guy has no morals. He’s a pleasure seeker who will do anything. In other words, he’s a bitch!”
“There’s no way someone as cute as him would do that…” is what Natsume believed at first until Haru intrudes into his home and tells him, “They found out that I was three-timing them, so let me stay over~!” After Natsume reflexively pins him down and they have sex, they end up becoming sex friends. Natsume doesn’t want just the pleasure, he wants to date Haru, but Haru doesn’t agree……
A pure love story about how a slow to mature ikemen and a cute playboy go from being sex friends to lovers.