This week viewers of the Channel 4 show have seen the pair's relationship buckle as she confronts him about his cheating.
But we can reveal Nicole, 19, knew exactly how far 24-year-old chef Rex will go to get the girl-because he nicked her from a pal.
A close friend of Rex revealed: "He was desperate to have sex with Nicole and didn't care about losing a friend he'd had for eight years.
"When it comes to a woman he wants, Rex will stomp all over anyone and doesn't care about the consequences. Nicole knows he can't be trusted."
Now friends fear Rex and Nicole are themselves heading for meltdown.
One source said: "Things are not looking good for Rex and Nicole. She put on a brave face when she first went in the house, but as the time has gone on she hasn't been able to resist challenging him about his behaviour."
Rex only met Nicole after being introduced by his friend, a club DJ known as Richie Rich, 25, whose relationship with her was on the rocks.
To try to win Nicole back, Richie took Nicole for a drink at Rex's dad's posh bar in trendy Notting Hill. But then the show-off chef muscled in.
The friend said: "Rex couldn't resist Nicole. She's gorgeous and was up for it. Rex fell in love with her straight away and before you know it they were really serious about each other. They kept it quiet for a couple of weeks. They were seeing each other on the sly because they didn't want Richie to know, but then he found out.
"Richie was really upset about the whole situation, just devastated. He still really liked Nicole and Rex was his best friend.
"He used to hang out with Rex all the time so seeing his best mate with the girl he loves breaks his heart."
Until Rex pinched her, Richie had been determined to rebuild their relationship. The pal explained: "Richie was taking Nicole out to show how much he liked her.
"One night Richie was boasting he had lots of rich friends and he took her along to meet Rex at his bar in Notting Hill.
"Nicole's got a taste for the high life and in that respect Richie was like a warm-up for Rex. Richie had VIP access in clubs but hasn't quite got the social standing like Rex who has got it all - bars, money and gentlemanly charm too."
Richie was furious about his pal's betrayal and tried his best to sabotage the relationship.
"He tried to break up the relationship a few times by telling people Rex had cheated on Nicole loads and is far from faithful," explained the friend.
Since Nicole joined the Big Brother house they have had a string of rows.
Earlier this week show bosses took two hours to convince her to stay after a bust-up with Rex over a story that he had bedded a stripper in Las Vegas.
But, despite the strains, one of Rex's close pals says their romance is set for the long term: "Nicole's definitely thinking about getting married to Rex.
"She already jokingly calls herself Mrs Newmark. Whether Rex is as keen is another question."