There was a lot of fun going down at Taylor Swift's star-studded birthday bash at the pop star's Tribeca apartment on Dec. 13. There were also tears and turmoil, as Swifts' best pal Selena Gomez shouted and cried about her on again, off again romance with Justin Bieber.

The dramatic and emotional party scene was described by a source in the new issue of Us Weekly. The source reveals while fellow partygoers like Beyonce and Jay Z enjoyed beers, pizza and sushi and mingled with pals like Justin Timberlake. Gomez--who has dated Bieber on and off for three years now--was reportedly getting emotional over the "Boyfriend" singer.

"She shouted, 'No one understands me! My boyfriend doesn't even understand me," an insider told Us, adding that bystanders--including guest Sam Smith--"just stared [at her]." 

Aside from the dramatic scene, which took place on the upper terrace, the rest of the party was having a "total blast," another source tells Us.

Taylor's bash--complete with a karaoke machine--kicked off after the "Blank Space" singer's performance at Z100's Jingle Ball. Guests at the birthday party included another of Swift's best friends Karlie Kloss, plus Kelly Osbourne, 5 Seconds of Summer, HAIM, Nick Jonas and Olivia Culpo, Charli XCX, Chrissy Teigen, Shawn Mendes, Ansel Elgort and Jaime King.