Kara Killmer shares the moment Brett knew he had to break up with Casey

This moment has been the pivotal moment in her decision to do

In Season 11, Episode 2 (which aired on September 28), we see Brett trying to work out her breakup with Casey through her paramedicine project.

But he told NBC that work will remain at the center of Brett's life, in spite of the split with Casey.

We'll see her really focus on herself and what she wants to do in life. I think we've seen her in a romance the whole time, but we should explore all of her other interests too.

Brett Killmer tells NBC Insider that the long distance between her and Casey made it hard for her to be "100 percent" anywhere. 

"She wasn’t able to be fully invested in her relationship or her work," she says. "And she had this passion project with pre-medicine that is really making a difference."

Brett broke up with Casey when they saw that Sheffield was engaged to someone else.

"Sheffield comes back basically to tell Sylvie, 'I'm engaged,'" she says. "I think that was one of the dominoes for Sylvie, a wake-up call."

"I remember when Sylvie was still frozen in her relationship. I believe she needed a push before moving on."

Killmer said that she was just as sad as the fans were when the show ended. Brett is taking steps to move on, which is a good thing to see.

To see what happens and catch up with past episodes, watch Chicago Fire on NBC Wednesdays at 9/8c and the day after via Peacock.