Koibito yo (1995)

Just hours before two different couples (Manae & Ryotaro : Shoko & Kohei) take their vows, Manae and Kohei discover an untold secret of their spouses-to-be. While they are pondering over their decisions, they meet each other and become friends. Their friendship then extends after their marriages with Manae taking the initiative of choosing her home beside Kohei's. This move is certainly not to Ryotaro's advantage, as he is Shoko's ex-boyfriend and the child she is carrying is actually his!