"I knew that he was feeling like making the switch," Courtney toldPeople. "I've never seen him so conflicted and sad."
Courtney apparently spent time with Arie after The Bachelor's Season 22 finale filmed in November 2017, when he proposed marriage to Becca Kufrin at the final Rose Ceremony in Cusco, Peru.
Courtney occasionally works with Arie in real estate in Scottsdale, AZ, and Arie also previously revealed he's Courtney's landlord.
"We talked through everything. I gave him the best advice I could give him. I encouraged him to follow his heart," Courtney disclosed.
After getting engaged, Arie decided that his heart truly belonged to his runner-up, Lauren, and so he blindsided and dumped Becca on-camera in early January and then begged Lauren to take him back days later.
"I felt sad for him," Courtney told People. "But I think he made the right choice in correcting his mistakes."
Lauren decided to give Arie a second chance, and then on Tuesday night's After the Final Rose special on ABC, the Bachelor popped the question to the blonde beauty. So Arie got engaged twice during his The Bachelor season.
Arie began dating Courtney, Ben Flajnik's ex-fiancee, in October 2012 -- only days after she called off her engagement from the Season 16 Bachelor. Although the romance didn't last long, Courtney revealed in February 2016 that she still liked to make out with Arie "from time to time."
The pair's dynamic confused fans for years, but both Arie and Courtney have insisted for a while now their relationship is completely innocent and platonic.
"I've been through [this process]. You go into this wanting this fairy-tale ending, and it's so rarely like that," admitted Courtney, whose engagement to Ben only lasted seven months.
Courtney watched Arie break up with Becca on-camera when ABC aired the first part of its two-night finale earlier this week, and she acknowledged it was "painful to watch."
"But he made a mistake. People make mistakes," said Courtney, a former model. "I don't think people need to pile on. He told me he filmed it so it would guarantee [Becca] as the next Bachelorette."
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But Courtney anticipated her pal would face a lot of backlash for his decision to swap one fiancee for another.
"I knew the storm was coming," Courtney insisted to the magazine. "It made me heavy-hearted for everybody. But after watching, I can tell he's so happy. I think he got what he wanted out of this. I can't fault him for that."