The 29-year-old interior designer fell for Swiderski on the fifth season of the ABC romance reality show and the couple later became engaged, although they announced their split earlier this year.
"It was the last thing I wanted to do. It's terrible to leave because the other person doesn't know what they want," she told the new issue of Us Weekly.
The star - who relocated to Chicago from Canada for the romance - reportedly added that Swiderski is "not a bad guy... he's just not quite ready to grow up".
At the time of the split, Harris was quoted as telling OK: "I love him and I'm really sad, but I have to look out for me", while Swiderski said: "Jillian isn't happy and I'm definitely sad about the whole thing, but we've got to work through some things on our own if we decide to move forward."