August 29, 2018 09:00 AM

After Miranda Lambert suddenly announced she was single, fans immediately began wondering what went wrong in her brief romance with Evan Felker.

Last week, the country superstar revealed in an interview with The Tennessean that she and the Turnpike Troubadours singer, both 34, recently broke up, but the reason behind the split instantly became a game of fill in the blank.

Now, a source reveals to PEOPLE that Felker crossed lines that caused their relationship to end.

“I don’t think it was a dramatic split, but he knew what he was ‘allowed’ to do based on her rules and he broke them,” says the source. “He did something that he knew she wasn’t going to approve of, she assumed he did it and he didn’t deny it.”

In May, multiple sources confirmed to PEOPLE that Lambert and Felker’s relationship took off after he opened with his band for three dates on her Livin’ Like Hippies tour in early February, just months before her split from boyfriend Anderson East was revealed in early April.

Jason Merritt/Getty; Frazer Harrison/Getty

“Love is a hard road sometimes and it’s been a roller-coaster ride for me, but I’m definitely thankful for all the ups and downs because I’ve had some really good songs come out of it,” Lambert said to The Tennessean. “You’ve got to take the bad parts and put them on paper and then move on to the happy parts.”

For more on how Miranda Lambert is doing after her split from Evan Felker, subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

Felker and Lambert’s budding relationship was a surprise to everyone, including his estranged wife Staci Nelson, 33, whom sources previously said he “ghosted” and then blindsided with his sudden divorce filing in mid-February — 15 days after he met Lambert in person for the first time.

On Aug. 17, an insider confirmed that Felker and Nelson’s divorce was finalized.

RELATED: Miranda Lambert Dating Turnpike Troubadours Singer Evan Felker After Anderson East Split: Report

“Staci very much believes in marriage and very much wanted hers to work,” says the source. “Lucky for her, the breakup happened a few days after the legal process was over and she felt no obligation to take him back.”

RELATED: Evan Felker’s Ex-Wife Defended Him One Day Before Miranda Lambert Split News

Though fans speculated that Felker and Nelson were back together after she defended her ex on social media when the Turnpike Troubadours dropped out of their final performances of Lambert’s The Bandwagon Tour, the source confirms “there is no reconciliation in the works.”

“Evan knows they were never gonna get back together,” the source adds.

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