The Oscar-winning actress, who recently separated from the dancer, was spotted on August 4 in Sydney, Australia, without her wedding ring. This outing came two months after reports that the choreographer, 46, had cheated on the Thor alum with climate activist Camille Étienne, 25.
"She doesn't want to turn her kids' world upside down," the source continued of why she's hesitant to split for good, referencing the couple's two children, Aleph, 12, and Amalia, 6. "It's very hard to imagine life without Benjamin."
The dancer originally met Portman in 2009 while doing choreography for the star's hit movie Black Swan, and they tied the knot in 2012.
"She loves Benjamin," they noted, mentioning that Portman's decision to at least separate was not an easy one. "So when he made all sorts of promises she agreed to try."
However, "it's starting to look like she can't get past the betrayal," the insider said. "She hasn't come out and said she's leaving him. But a lot of people suspect that's where this is heading. It's not looking great."
As OK! previously reported last week, a source said the pair had separated due to his infidelity.
"After news of his affair came out, they've been trying to work on their marriage but are currently on the outs," they shared.
Prior to these claims, another insider explained, "Natalie believes Benjamin's affair was a brief and stupid liaison that means nothing to him," adding that she was still "humiliated" by the rumored cheating.
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Despite this, Portman reportedly wanted to see if he's "capable of rebuilding her trust" because she didn't want her kids to "grow up in a broken home."
Star reported on the source's comments.