According to Us, Flajnik started cheating after he returned home to San Francisco and he began seeing the televised behavior of Courtney Robertson, the controversial The Bachelor bachelorette he reportedly proposed to when his final Rose Ceremony was filmed on November 16.
"Ben began having issues with what he saw," an insider told Us. "[But] instead of talking to Courtney about it, he just started avoiding her. They haven't split, but he basically stopped talking to her. He buried his head in the sand."
Instead, Flajnik reportedly started hanging out at San Francisco nightspots.
"He's drinking and hitting on women, and pretty much acting like a single guy," a source told Us.
Flajnik has become a frequent visitor to Monaghan's, a dive bar that draws "adoring Flajnik fans wearing skimpy clothing," according to Us.
While there on February 17, Flajnik and a "few friends" reportedly chatted up numerous women before leaving around 2AM with four girls -- two forThe Bachelor star's friends, and two for Flajnik himself.
"Ben seemed pretty toasted, and this woman in red pants came up to him," a witness told Us. "It looked like an altercation at first, then he kissed her on the mouth and hugged her. She wrapped her arms completely around him and embraced him. After the kiss, she walked the other way."
After visiting a donut shop, the Flajnik and the group reportedly headed to his apartment as The Bachelor star enjoyed the company of another girl he had reportedly been texting since meeting in Las Vegas on Valentine's Day.
"Ben and this girl looked like they were drunk and having a good time," the Us witness said.
However, Flajnik reportedly had to make a pit stop along the way and "stopped to urinate against the side of a building." The incident apparently wasn't a turnoff for the woman, according to Us, which reported she spent the rest of the night at Flajnik's apartment and was seen leaving the following morning.
The next night, Flajnik was also reportedly spotted publicly making out with another woman for nearly two minutes while he and the woman were walking his dog Scotch at a nearby waterfront park.
"The woman's hands were all over Ben's body and his hands were on her ass the entire time," a source told Us.
Flajnik and the woman then reportedly walked "arm in arm" back to his apartment, where she also reportedly spent the night.
"She looked tired [when she left in the morning]," a witness told Us.
Us published several photos of Flajnik and the three women, however Flajnik's representative has denied The Bachelor star has been cheating on his fiancee.
"The photo is of two friends who have known each other for years and are together in a social setting, surrounded by a group of friends. Ben did not take any girls back to his apartment alone. It was a group setting every time. Ben has never condoned cheating," the rep told Life & Style.