The Other Man (2008)

Genre: Drama
Starring: Antonio Banderas, Laura Linney, Liam Neeson, and Amanda Drew
Tagline: Is knowing the truth worth living a lie?

Plot: The story of a husband who suspects his wife of adultery, and sets out to track down the other man in her life

http://www.imdb.com/title/tt0974613/
http://en.wikipedia.org/wiki/The_Other_Man_(2008_film)