When you're dating an actor, it's always uncomfortable to watch him get cozy with an on-screen lover - especially when that lover is an ex! That's exactly what Jessica Biel will have to deal with when she watches Justin Timberlake and his ex-girlfriend Cameron Diaz onscreen -- and in bed together! In the upcoming romantic comedy Bad Teacher, Cameron plays Elizabeth, a recently dumped school teacher determined to score a date with Justin Timberlake's character, Scott, a fellow teacher already in a relationship.

Life & Style has exclusively obtained a copy of the movie's script -- and in it, things get awfully steamy. In one scene, the real-life exes are alone in a hotel room and begin, as Justin's character puts it, "dry humping." Justin winds up getting, well, way too excited way too soon -- ending their make-out session prematurely. "That was a mistake," he says, rolling off her. "That was fast," she responds.

For more on Cameron and Justin's steamy sex scenes, pick up the latest issue of Life & Style, on newsstands now.

Photo Credit: Startraks