Three (2004) ending / spoiler
Jack finds out his wife's been sleeping with Mannuel and is naturally pissed. He overhears them planning to steal the boat he's found and been patching up. He sabotages it to sink but they manage to struggle to shore. A fight breaks out between Jack and Mannuel, until Mannuel tries to drop a rock on Jack's skull which overbalances him and he falls back onto a broken off tree branch and is impaled through his chest. Soon after Jennifer is rescued but lies about being the only castaway leaving Jack stranded. As the boat heads off into the distance Jack surfaces from his deep sea fishing, to see he's been left behind.
Submitted by THE TRUTH HURTS