Originally posted by US Weekly

COVER STORY: Can she trust Justin? Do cheaters ever change?
It took a bitter breakup and an ultimatum to get playboy Justin Timberlake to propose. Now Jessica Biel will find out if a cheater can ever change.



They looked like any other vacationers gearing up for a run on the slopes, outfitted with goggles, knit caps and gloves at the Rainbow Lodge in Big Sky, Montana's swank Yellowstone Club. But newly engaged couple Justin Timberlake and Jessica Biel were not their usual outgoing selves. "Justin was always sitting next to Jessica when they were relaxing in the lodge," says a witness at the resort, where the duo cocooned themselves for the holidays before jetting to Las Vegas together January 9 for the International Consumer Electronics show. "They just seemed to be enjoying each other's company."

But can one idyllic trip offset four years of heartbreak and drama? "They seem really happy and in love right now," says an insider of the duo, who split for three months last spring in the wake of reported infidelities on his part. Yet as Timberlake, 30, and Biel, 29, attempt to put his promiscuous past behind them, insiders are concerned their happiness won't last. "Everyone knows his track record, so her friends are skeptical of the engagement," says the source. "But Justin worked hard to get her back after they split, so we'll see."

HER ULTIMATUM

When the two got back together in June, Biel was finally in the driver's seat. "Justin came back to her, with his hat in his hands," says a source close to the New Year's Eve actress. "It had hit him that she was the one for him. But she was having fun in Toronto with Collin Farrell and was ready to move on." So before she agreed to give the relationship another round, she laid down the law: aisle or exit. "There was a lot of discussion on where they were going," says the source. "Marriage was definitely a part of that" - the most important part, the Timberlake source insists. "She fully gave him an ultimatum," declares the source. "It was understood that he was going to propose."

And she needed to be sure she could finally trust him to be faithful. "Everyone knows Justin has a wandering eye, and Jess knows too," admits the Biel source. But, as another insider explains, she never had to face the problem because she never saw any incriminating photos or texts. "Jessica turned a blind eye," says the source, "because she really wanted to stay with him."

The charming Timberlake "convinced her that he wants to make this work too," says the Biel pal. "There is no way Jessica will deal with his straying eye now that they're engaged. You are going to see some changes from Justin."

HIS SKETCHY PAST

A-list Flirt Alert
The star certainly doesn't lack confidence!

MILA KUNIS
He was "smitten" and pursued her.

SCARLETT JOHANSSON
Last he, he and his "What Goes Around... Comes Around" love interest, 27, partied until the wee hours at an NYC club, says a source.

OLIVIA MUNN
In October 2010, a source reveals, he and the actress, 31, "spent an intense three days together, basically just having sex the whole time."

KATE HUDSON
Timberlake and reported former flame Hudson, 32, cozied up at NYC club the top of the Standard on December 10, 2009.

CIARA
She licked him in her 2009 "Love Sex Magic" video.

RIHANNA
Another sexy video, another pass! His "Rehab" costar, 23, in 2008, said, "I'm close with Justin."

But just how much can an A-list Romeo, nicknamed "Trousersnake" by the press, really change? While the actor is trying to reform, sources say he can't simply turn a 180. Though the sporty pair often seem united - they campaigned for Barrack Obama together in 2008, and Timberlake himself gushed to "Vanity Fair" this June, "She is the single-handedly most significant person in my life" - temptation has historically bested his good intentions. "Justin really loves Jessica, but he just can't stay monogamous," explains the Timberlake source. "Basically, his brain and his penis operate separately, and the brain proposed to her. He thinks it is what he wants, but he has two sides - and the other will pop back up. He has a big sexual appetite."

And his friends certainly aren't going to help him reform. "He's surrounded by a bunch of people who would do anything to stay in his good graces," reveals a source. "They're so afraid of being booted out of the circle, they'll hide all his secrets. He has quite a few, after all. As recently as September, Timberlake partied the night away at NYC's 1Oak with reported former flame Scarlett Johansson, 27 - even going back to her penthouse apartment. "They were hard-core flirting," says a witness. (Reps for both denied cheating.)

And this encounter was after "US" broke the news of his three-day hotel tryst with Olivia Munn, 31, in September 2010. (For her part, Biel believed Timberlake when he told her the Munn incident was "hear-say," says a pal.)

Then of course, there are his layman conquests. The most blatant? According to a source, the head-turned hooked up with a woman in an NYC bar just 15 minutes after meeting her in 2007. He "found her Southern accent irresistible," says a source, adding that her rejoined his friends at the bar post-interlude.

But now that she's a bride-to-be, Biel has a strategy to keep him stray-free. She's smart. She knows she's going to have to limit the amount of time that Justin spends with his old clubbing friends," says a Biel source. But friends wonder if her constant monitoring will work long-term. "Jessica has made it easy for him to behave because she's controlling," says a Timberlake pal. The confidant of the former boy bander even confesses," "I don't think he's been tamed." At most, the source says, "I think he'll be more strategic about his affairs, maybe do it less."

THEIR SHAKY FUTURE

Together as fiancées, the pair started 2012 off on the right snow boot. Ensconced at the Yellowstone Club, they stayed to themselves, apart from joining Bradley Cooper and new squeeze Zoë Saldana plus Leonardo DiCaprio and his girlfriend, Erin Heatherton, for lunch at the resort December 26. Often snowboarding and spending quiet time with Timberlake's manager and her family, the two largely retreated into their own little world."

But with work looming large on the calendar for Biel, their private bliss won't last long. The actress is set to start filming the thriller "Emanuel and the Truth About Fishes" in L.A. January 24. For his part, the Grammy winner will be on set more too. "He wants to focus on his film career more than music for now," says a source. (Next up: the 2013 flick "Inside Llewyn Davis" with Carey Mulligan.) That's fine by Biel, acknowledges the insider: "He can be in one place for longer periods and not have to tour."

And his growing movie-star status perfectly suits her future plans. "There's been no ultimatum about it, but Jessica definitely wants kids," says a Biel pal. But can she persuade Timberlake to get family-focused next? Says a Biel source: "Jess has always been optimistic when it comes to Justin."

WHAT CAMERON THINKS

"Cameron never wanted to marry Justin," snips a pal of the actress, 39, who dated Timberlake for four years. "But she's shocked he proposed. She knows too well Justin is a dog." The pair split in early 2007 and he soon took up with Biel - prompting Diaz to scream, "Is this your new f--king girlfriend? Look at her!" to the couple at a Golden Globe party. But another pal says Diaz has moved on: "She's happy for them. She and Justin are actually good friends."

Originally posted by Duca

the head-turned hooked up with a woman in an NYC bar just 15 minutes after meeting her in 2007. He "found her Southern accent irresistible," says a source, adding that her rejoined his friends at the bar post-interlude.

Originally posted by IVY

she deserves so much better