Koibito yo My dear lover (1995)

Just before two different couples (Manae and Ryotaro : Shoko and Kohei) are married, Manae and Kohei discover a secret of their spouses-to-be. While they are pondering over their decisions, they meet each other and become friends. Their friendship continues after their marriages with Manae choosing her home beside Kohei's. This certainly complicates things for Ryotaro, because he is Shoko's ex-boyfriend and the child she is carrying is actually his.