Tulisa Contostavlos and Fazer have reportedly separated
The N-Dubz bandmates - who have known each other since they were 11 years old after forming the group with her cousin Dappy Contostavlos - are said to have broken up after a series of arguments.
A source told the Daily Mirror newspaper: "It`s all over for Tulisa and Fazer.
"Fazer has been out clubbing twice this week without Tulisa, and she, too, has been spending more time with her friends away from him.
"They are insisting nobody else is involved and clearly don`t want to stick the knife in to each other because they`ve been close since they were 11.
"They`ve still got a lot of respect for each other, but they`ve had a very turbulent relationship."
The 23-year-old `X Factor` judge and the music producer - who sparked rumours they were getting engaged just weeks ago - have threatened to split up on more than one occasion following an argument, but insiders believe they are over for good as she needs to keep a "clean-cut" image for her career.
The source added: "They`re both very feisty and not scared to speak their mind, and one of them will often storm out and tell the other their relationship is over during their fiery rows.
"But they really do sound serious this time. It wouldn`t be out of the ordinary if they changed their mind in a week or two and got back together but their closest friends feel it`s different this time.
"Tulisa was successful with N-Dubz, but `X Factor` has turned her into a household name and she can`t afford any damage to her image.
"It`s important that she is reasonably clean-cut, and Dappy and Fazer can sometimes push the boundaries."
The couple are said to have split on a recent holiday to Barbados, where they were thought to have been "arguing the whole time", but Fazer has told friends he now wants her back.
A source told the Daily Star newspaper: "They were arguing the whole time they were away and haven`t managed to sort things out.
"Since they got back Tulisa hasn`t been staying in the flat they share, choosing instead to stay with her PA to give her some much-needed space.
"Fazer has been staying with a friend too. But he`s has been telling people in his circle that he still loves her and wants her back."
Tulisa was spotted partying at London`s Maddox club with friends on Saturday night (21.01.12), while Fazer - whose real name is Richard Rawson - spent Wednesday night (18.01.12) at London`s Aura nightclub and Saturday at Club 55.