Say Nothing (2001)

Housewife Grace Needham (Nastassja Kinski) has a one-night stand with Julian Grant (William Baldwin), who then becomes obsessed with sinking her marriage to husband Matt (Hart Bochner). The twist here is that Julian is a millionaire global powerbroker, and Matt works for him! It's a titanic battle of testosterone as the guys duke it out while Grace simmers angrily.