Though her rep vehemently denied it earlier this week, UsMagazine.com reports Jennifer Aniston is dating Justin Theroux. The two are co-stars in the upcoming film, 'Wanderlust,' which recently wrapped filming.

"Jen is totally into him," a source told UsMagazine. "They have been hanging out for months. She wants to be with him all the time. She's diving in headfirst," the source added.

The rumored couple was seen together at the Sunset Tower Hotel in L.A. last week and X17Online.com reported that a source said the dinner date wasn't the first date for the couple, and that they have been on dates previously.

The source told them, "Jen and Justin have recently started dating. They've known each other for a while, but they're more than friends now. They're cautious -- they're both taking it slowly."