Leighton Meester and Blake Lively "avoid each other like the plague,"

An insider also tells OK! that Leighton "is jealous of everyone. She doesn't like her character's wardrobe. She thinks it's conservative and she's more fashionable and sexy in real life. She once said, 'I look like a dork in my outfits.'

"She wants to be a movie star and wants the publicity that her co-stars are getting," says the insider. Leighton's rep denies the claim.

The source also confirms, "Penn Badgley and Blake are a couple and so cute. They hide it from cameras and go to dive bars and stay out of the limelight. They're low-key, but such a happy couple."

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