Natsume Wants to Blossom [Natsume Wants Book 2] (manga)

Thanks to his housekeeper-turned-boyfriend, Natsume has finally learned just how enjoyable sex can be and abandoned his misguided plans to get back at his ex. Instead, he’s come up with a new agenda: this time, his goal is to become a lover worthy of his beloved Kou. Yet in the midst of his planning, Kou’s childhood friend Kurumi returns to Japan, and the future of Natsume’s budding relationship is thrown into jeopardy!