Why Adam Levine Exercised 'Bad Judgment' and Crossed a Line in His Marriage: Source

More is coming out as to why Adam Levine "crossed a line" in his marriage amid allegations he communicated with women that were not his wife.

On Monday, the 43-year-old Maroon 5 frontman denied having an affair but confessed to "crossing a line" in his marriage to Behati Prinsloo when he had "inappropriate" conversations with other women.

Now, a source close to Levine tells PEOPLE despite claims by an Instagram model that they had an affair, the rocker insists to those around him that "nothing physical happened. He swears it."

"He was messaging her, being flirtatious with three women. One of them — she specifically said they have a physical relationship but he is completely denying that to friends," the source adds.

RELATED: Adam Levine Is 'Trying His Best to Make Things Better' with 'Very Upset' Behati Prinsloo: Sources

As for why the singer had flirtations outside his marriage, the source says Levine craves "female attention."

"Why would he do this? He liked the attention," the source tells PEOPLE. "He likes it more than most."

Amy Sussman/Getty Behati Prinsloo and Adam Levine

The source adds that "during COVID-19" Levine "was isolated," however he and Prinsloo, 34, "definitely didn't break up and they weren't on a break."

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Cheating accusations against Levine spiraled after Instagram model Sumner Stroh claimed in a now-viral TikTok that she had a year-long affair with Levine. Stroh did not provide dates as to when the alleged relationship took place, but shared screenshots of apparent Instagram DMs from the musician, including a note from April after she claimed they'd stopped speaking.

She also shared a message allegedly from the singer in which Levine appears to ask if she would be okay with him naming his and Prinsloo's unborn baby Sumner.

The source tells PEOPLE that the request showed "very bad judgment."

Adam Levine/Instagram

RELATED: Adam Levine Denies Having an Affair but Admits He 'Crossed the Line' After Cheating Accusations

"People don't know what he was thinking," the source says regarding the baby's name.

Levine and Prinsloo, married in 2014 are parents to daughters Dusty Rose, 6 this month, and Gio Grace, 4, and are expecting a third child.

RELATED VIDEO: Adam Levine and Behati Prinsloo Expecting Third Baby

Addressing the rumors in a statement shared on Instagram Tuesday morning, Levine wrote, "A lot is being said about me right now and I want to clear the air. I used poor judgment in speaking with anyone other than my wife in ANY kind of flirtatious manner. I did not have an affair, nevertheless, I crossed the line during a regrettable period in my life."

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He continued, "In certain instances it became inappropriate; I have addressed that and taken proactive steps to remedy this with my family. My wife and my family is all I care about in this world. To be this naive and stupid enough to risk the only thing that truly matters to me was the greatest mistake I could ever make. I will never make it again. I take full responsibility. We will get through it. And we will get through it together."