The source explained Tayshia, 28, and Chase, 30, dated for 10 months and talked about "engagement and marriage" before her stint on The Bachelor.
"It's a messed-up situation," the source told the magazine. "He was in love with her. He's not anymore, but he still loves her."
The former couple allegedly got off to a slow start, however, because Tayshia "wasn't completely ready for a relationship" when she first met Chase.
Tayshia was still reeling from her divorce at the time from Josh Bourelle, who filed the divorce papers in October 2017. Tayshia told Colton on The Bachelor season she put all of her efforts into saving the relationship but couldn't force her spouse to want to be married.
Chase opened up to Us about his relationship with Tayshia, saying they met at a bar in their hometown of Newport Beach, CA, in November 2017.
"We fell in love really quickly," Chase insisted.
While Chase and Tayshia were reportedly hesitant to label their romance early on, he said they had an understanding neither of them was "dating anybody else."
After months together, Chase posted an Instagram photo of the former couple kissing in July 2018 and claimed they were planning to "do something special" for her birthday in September 2018, just weeks before she entered The Bachelor mansion.
"I moved some things around... before she ended up deciding to leave [for The Bachelor], because she still wasn't really sure if she was going to go on the show or not," Chase explained.
FOLLOW REALITY TV WORLD ON THE ALL-NEW GOOGLE NEWS!
Reality TV World is now available on the all-new Google News app and website. Click here to visit our Google News page, and then click FOLLOW to add us as a news source!
"She was still back and forth... she wasn't sure. As it got closer, I could kind of see changes between us and I could kind of tell that she was leaning toward going. I don't know all of the exact reasons for that."
Tayshia is one of four bachelorettes still in the running for Colton's heart, with the women's round of hometown dates right around the corner.
Tayshia admitted in a previous episode she was falling in love with the 26-year-old charity founder and former pro football player at this point in the journey.
While viewers have to wait a few more weeks to see how Colton's season ends, the source told Us that Tayshia contacted Chase once filming concluded late last year.
"She called him and he saw her," the insider noted. "It's just hard for him to talk to her."