My Brother's Lover (1998)

Kenji breaks up with his girlfriend and goes to stay with his brother, Ryosuke, who is married but is having an affair with a local waitress. It becomes clear quickly that Ryosuke is unhappy with his marriage to Haruyo, who desperately tries to get them to reconnect. One night Kenji goes out alone, to see the mistress of his brother...and they fool around.