"The backlash from the show was too hard on both of them," the source explained.
"They decided to split and focus on themselves. Pieper thinks it's best for her to spend time reevaluating her life."
The source added of Pieper, "She thinks this is a good life lesson, but wants to move on."
On Bachelor in Paradise's currently-airing seventh season, Pieper and Brendan were accused of bringing their established pre-show relationship to Mexico so they could continue dating on television and gain more fame and social-media followers.
Brendan led his fellow cast members to believe he and Pieper had only hung out a couple of times and developed a surface-level connection when he was living in the Boston area, but Pieper admitted they had enjoyed about 10 dates and were together "without labels" before filming commenced.
Once Pieper left Oregon and entered Paradise with a Date Card, she immediately asked Brendan out without even considering another man on the beach.
During the couple's first date in Mexico, Pieper thanked Brendan for "playing the game," referring to how Brendan admitted he had to "navigate" the Paradise process and do "certain things" to ensure they'd be on the beach at the same time.
Prior to Pieper's arrival, Brendan had exchanged roses with Natasha Parker, who really liked Brendan and felt lied to, betrayed and manipulated.
After spending several hours together in Paradise, Pieper called Brendan her "boyfriend" and she and Brendan laughed about how Brendan had "incriminated" himself and would probably look like a jerk on TV this summer.
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Pieper referred to Brendan stringing Natasha along as "heavylifting" and bragged about her influencer status and having tens of thousands of Instagram followers, and Brandon called Natasha "annoying" when both individuals had their microphones on.
After the footage aired of Brendan crushing Natasha, he lost more than 100,000 followers and Pieper's follower count also dropped by around 10,000. As for Natasha, she gained a whopping 400,000 followers or so.
But Pieper has also said she doesn't have "any regrets" and that Natasha had allegedly been made aware of Pieper and Brendan's pre-show romance before Paradise's seventh season even began filming -- a statement which Natasha subsequently denied.
Brendan and Pieper were essentially pushed out of Paradise after upsetting and frustrating their Bachelor in Paradise co-stars, but Pieper told Us Weekly last month that she and Brendan were "working through things."
"This obviously isn't something that's super healthy for a relationship either, so it kind of is what it is. Every day, [we're] taking it day by day," Pieper revealed at the time.
As for Natasha, she recently complained to Entertainment Tonight that Brendan's "disregard for a human" was "the most shocking, awful thing" of the whole scandal.
Natasha accused the commercial roofer of "making a mockery" of their short-lived romance on Bachelor in Paradise, adding, "He just seems like a very selfish person. And that's my biggest takeaway from who he is: selfish."
Natasha seemed furious, for instance, that Brendan accused her of having "selective hearing" when they'd talk about their relationship because he claimed they were nothing more than friends the entire time.
Brendan also insisted Natasha had no other "prospects" on the beach, suggesting she should have been thankful to receive his rose when there was allegedly no romantic spark between them.