The couple announced their breakup on social media last week.
The Bachelor couple announced their split via social media just days ago, and now a source close to the situation tells ET that things broke down for Peter and Kelley right before their long-planned move to New York City, which they'd spoken to ET about in July.
"The move was the final straw in some ongoing issues in their relationship; the biggest of which was that they were not on the same page about how they approached relationships," the source explains.
ET's source says, that despite some online speculation, cheating wasn't to blame for the couple's separation, adding that while Peter brought up the breakup, Kelley had also known there were issues for some time.
"There was growth that needed to happen from Peter that wasn’t happening," the source adds.
But one Bachelor Nation rumor does seem to be true: our source says Peter's mother, Barb, was a "major issue" in the couple's relationship.
"Barb was very involved and expected to be a major priority within Peter and Kelley’s relationship," the source says.
In an exclusive statement to ET, Peter says, "Kelley and I broke up two weeks ago. I flew to Chicago and was finished with the relationship, then my mom really encouraged us to be in the relationship if we wanted to be and to not give up. Kelley and I operate on two different frequencies, and one isn’t better or worse than the other; we’re just two different people, and those differences surfaced after eight months of dating. But I loved her like crazy, and my mom really cared about her."
Fans of the Bachelor franchise will no doubt remember Barb from her emotional moments during Peter's season in early 2019, and her jaw-dropping appearance on the After the Final Rose special, where she strongly disapproved of Peter's relationship with Madison Prewett. When his relationship with Madison ended shortly after, Peter insisted that his mother's influence had nothing to do with their breakup.
"People will have their opinions but this is just between the two of us, and it's just a mutual respect and love. That's all," he said in a paparazzi video obtained by ET at the time.
Barb was notably a big fan of Kelley -- having picked her as a favorite during Peter's season -- and shared a heartfelt comment on her son's post about the breakup.
"Love can be fickle and it is not for the timid," she wrote. "Those who have experienced it know this all too well. But it is better to have loved and lost, than never to have loved at all. Our hearts ache for you two. Kelley will always have a piece of our hearts and we wish her only the best. Mom and Dad."
Days after Peter announced the split -- saying that while the couple "decided to go our separate ways," he would always have a "special love" for his ex -- Kelley took to Instagram to share her own feelings.
"I know a lot of you have already heard the news, but I wanted to take some time to process it for myself before sharing," wrote the 28-year-old attorney. "It saddens me to say this but Peter and I have decided to go our separate ways."
"Peter and I had some unbelievable times together and they will definitely be missed. Unfortunately him and I are in two different stages of our lives and saw our future paths differently," she explained. "I wish Peter the absolute best and want to thank everyone for your continued support as I move on to my next chapter. I’m still hoping to make it to New York one of these days, but for now I just want to focus on my happiness! 2021, I can’t wait to see what you have in store!"
While his season of The Bachelor saw Peter giving his final rose to Hannah Ann Sluss (and then briefly reuniting with Madison), Kelley was an early favorite. Peter and Kelley later reconnected after the show, with Peter previously telling ET that he was still "working to make it up to her for not picking her."
In November, the pair dispelled engagement rumors, with Kelley exclusively telling ET, "We are loving continuing to get to know each other, having lots of great adventures and growing together. We are very happy!"
For more on the former couple, watch the video below.