While her Heart Wants What It Wants, seems Selena Gomez’s love for Justin Bieber is also a bit of a party pooper.

US Weekly reports the 22-year-old broke down during best friend Taylor Swift’s birthday over her on and off again relationship with the Baby singer.

While the likes of Justin Timberlake, Jay Z, Beyoncé and Sam Smith partied the night away on December 13 at Taylor’s New York pad, Selena was having a lot less fun.

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Miss understood: Selena Gomez, pictured December 5, broke down during best friend Taylor Swift’s birthday last week over her relationship with Justin Bieber

The Spring Breakers star mustered a smile in photographs that popped up on Instagram, the magazine reports she was miserable during the 25th birthday celebration.

A source revealed the star became very emotional over the Boyfriend singer before she ‘cried and threw a fit’ on a top terrace at the apartment.

The insider revealed: ‘She shouted, ”No one understands me! My boyfriend doesn’t even understand me.”’

Smiling through the pain? The Spring Breakers star mustered a smile in photographs that popped up on Instagram, the magazine reports she was miserable during the 25th birthday celebration on December 12

Fun times: Besides Selena, guests (L-R)  Karlie Kloss, Danielle and Alana Haim, Jay Z, Beyoncé, Justin Timberlake, Sam Smith and Este Haim seemed to be having a blast

While confirming once and for all her and the 21-year-old pop star are back on, her outburst left others shocked.

‘Everyone just stared.’

Fortunately the birthday girl did not notice as she was too busy with her high profile guests, who also included Karlie Kloss, Chrissy Teigen, Kelly Osbourne and band Haim that had performed with Taylor earlier at Z100’s Jingle Ball.

She’ll cry if she wants too: The 22-year-old, seen leaving the bash, reportedly shouted, ‘No one understands me! My boyfriend doesn’t even understand me’

The Blank Space singer and her guests munched on eight bags worth of sushi and 20 pizzas that they washed down with Stella Artois beer, according to the insider.

It was particularly lucky that Taylor was not privy to the incident, as Justin has been a source of contention between the two pals previously.

While the outburst suggests Selena and Justin are once again back on, just two months ago they appeared to be off with Taylor suggesting Selena just focus on herself for a while.

A source told Hollywood Life: ‘[Taylor] wants her to at least try taking a year off dating. She thinks she should date herself for a while, take the time to get to know herself and appreciate herself.

Trouble when he walked in? It was particularly lucky that Taylor was not privy to the incident, as Justin, pictured December 7, has been a source of contention between the two pals previously

‘But she’s not going to force it, she’s trying to lead by example this time, instead of forcing her ideas down Selena’s throat, she realises she can be kind of pushy and she’s working on that.’

And Taylor wants her bestie to join her in New York away from Justin and the Hollywood heat.

Selena told Ellen DeGeneres: ‘She wants to kidnap me. She’s been begging me every time we get on the phone, because it’s been a really good thing for her.

‘You know, we’ve been friends for seven years and she really feels like she kind of stepped into her own and became a woman there, and she’s like, ”Alright, your turn!”’

On and off again: The Heart Wants What It Wants singer’s emotional response confirmed she and her beau, pictured October, are dating again

Src: dailymail.co.uk