Man, this is not the week to be in a relationship with a Gossip Girl co-star.

Yesterday, we reported how Jessica Szohr and Ed Westwick reportedly packed it in after her alleged flirting with one of his friends. Now more trouble in paradise.

A source says that Gossip Girl's Leighton Meester has broken up with her longtime boyfriend, Sebastian Stan, who plays a recurring character on the CW series.

Here's a photo of the attractive, possible former couple ...

Is it all over for Lebastian?

The starlet and aspiring pop star (one of her songs will be featured on next week's episode, as others have been in) "doesn’t know how to be in a relationship."

To top it all off, "she doesn’t really like them,” a source told OK!.

Well, that can never be a good sign for a guy trying to date her.

In other Leighton Meester news, it's her birthday today! Out of the way, Kristen Stewart! Okay, don't get out of the way, you're cool too. But make some room.