EXCLUSIVE: Secrets of Jennifer Garner and Ben Affleck's Romance — From Her Sneaky Visits to Bachelor Pad to How PDA Was 'Her Way of Telling World She's Forgiven Him'

As Jennifer Garner adjusted her stance and aimed her paintball gun on the grounds of Combat Paintball Park in Castaic, California – where her family gathered on March 2 to celebrate son Samuel's 13th birthday – Ben Affleck moved in.

Sliding an arm low around his former wife's waist, the Oscar winner angled his pelvis against her hip and pulled her in. It was a surprisingly charged embrace for the longtime, friendly exes. An observer told RadarOnline.com it was clear there were "sparks" flying, adding that the two were "giggling and joking and having a great time with each other."

Nearly 10 years after announcing their split following a decade of marriage, the 52-year-old Hollywood A-listers appear to have taken their amicable coparenting of Samuel, Violet, 19, and 16-year-old Finn to a whole new and unexpected level.

"It's no secret Ben's been leaning on Jen more and more since he split from Jennifer Lopez last year," a source said. "It's hard not to notice how close they've gotten."

With this new PDA, however, said the insider, "there's been a lot of buzz that they could be rekindling the romance, judging by all the time they've been spending together and their cozy behavior at the paintball park." Notably, the rendezvous came barely a week after Affleck's divorce from Lopez 55, was finalized.

The pair's giggly encounter made their connection clear; but experts told RadarOnline.com even more truth is in the details. The Air star's pelvis – first posture, for instance, "communicates his desire to be sexually intimate or a familiarity with her based on their old relationship," body language pro Patti Wood, author of Snap: Making the Most of First Impressions, Body Language and Charisma, confirmed.

She continued: "His hug is not something you do with an ex," she continued. "Wrapping his arm all the way around the front of her body, with the position of his pelvis and ventral front and heart window in contact with her body, it all infers a familiarity and desire for sexual ownership."

That's rich, considering what Affleck has put Garner through. Five years after the pair announced their split amid rumors of infidelity as well as his struggles with gambling and alcohol addiction, Affleck admitted to The New York Times that their divorce, finalized in 2018, was the "biggest regret of my life."

Despite his foibles, Garner also mourned the marriage. "I didn't marry the big fat movie star; I married him. And I would go back and remake that decision," she famously told Vanity Fair months after their split, lamenting: "He's the love of my life. What am I going to do about that?"

Their union may have ended, but her support didn't. She even drove him to rehab after their split and reportedly allowed him to live on her property before she moved into her new $7.9million farmhouse in 2018.

"Jen is a nurturer and can't help but worry about Ben. She's been his rock all these years," the source said. "She'll always forgive Ben, because he's the father of her children. She wants to help him be the best man he can be."

The insider added Affleck, who's reportedly been "casually dating" since his split from Lopez, relishes the sense of stability he has with the mom to his kids. "He's happiest when he's with them," noted the source. "There's nothing he'd like more than to make their family complete again."

For Garner, that's a risky proposition. One obvious reason is her nearly seven-year romance with tech business investor John Miller, whom she began dating in 2018. While the Cali Group and PopID CEO has stuck with Garner while she repeatedly tends to her ex, he's long hoped the Yes Day actress would take a step back from her ex, especially now that he's divorced from Lopez.

"John wants Jen for himself," an insider told one news outlet, adding that the businessman "is trying to deal with the duo's relationship by mostly staying quiet, but it's very hard to do that."

Over the last year, the Deadpool & Wolverine actress has been photographed with Affleck more often than with her boyfriend. In January, the Argo actor-director even evacuated to her house during L.A.'s wildfires. They fed the homeless together on Thanksgiving morning, then shared a holiday meal at Garner's home that afternoon.

And during their kids' summer break, they vacationed together in Japan. Garner was also spotted making a stealth visit to Affleck's place on his birthday in August – two months after she was photographed letting herself into the bachelor pad he was renting following his April separation from Lopez.

Despite speculation they're rekindling, the source said Garner is leery. On a November episode of the Lipstick on the Rim podcast, she shared some relationship advice from her mom, Pat Garner, who warned her, "Don't marry a man thinking you can change him."

Experts echo that motherly counsel.

"We're always tempted to go back to a past relationship because we want to prove that the other person really did love us after all," Beverly Hills psychiatrist Carole Lieberman, who doesn't treat the pair, told RadarOnline.com. "But there are pitfalls, and Jen should be very wary of getting back together with Ben, because a rebound relationship with him wouldn't last."

Friends feel the same, too. "Jen's pals are watching this play out with some concern. They think she's always been lacking in self-defense mechanisms when it comes to Ben. She's such a nice, caring person that she's become blind to his shortcomings," explained the source.

"They worry he'll let her down by embarrassing or humiliating her again."

There's also concern that if Garner won't set boundaries, Miller will. "John's been extremely patient, but how long he'll continue to be is anyone's guess," the insider continued.

Indeed, some in Garner's circle believe she would have married her boyfriend long ago if it hadn't been for her unfinished business with her ex.

"No one would blame John for making Jen choose, but any ultimatum could only lead to heartbreak," the source added.