Down South Where The Lemon Trees Blossom(1992)

Kimi yo Shiruya Minami no Kuni

Kouji and Takayuki are childhood friends. They were born on the same date, hospital, and almost at the same time. Even their mothers are best friends, so it's a given that the two of them are together at almost everything to the point they even promised to marry each other by the time they turn 15. The problem is Kouji and Takayuki are not quite on the same page. While Takayuki is going to all lengths to keep the said promise and be together, Kouji's slow-on-the-uptake personality and certain real-life factors make him hesitant about everything. Why is everything suddenly so complicated?

(Source: Manga Planet)