The woman who moved in with her ex-husband and his new wife for the sake of their kids just welcomed another new roommate: her boyfriend

• In September, Katie Mathis moved in with her ex-husband and his new wife to parent their three daughters.
• The arrangement went viral on TikTok and has become more unconventional with her new boyfriend moving in.
• It hasn't been seamless, but the happiness of her kids "makes the harder moments worth it," she told Insider.

Roughly one month after announcing she was moving in with her ex-husband and his new wife to co-parent their three daughters full-time, Katie Mathis has welcomed another new roommate into the fold: her boyfriend of one and a half years. The two live in a detached apartment above her ex's garage.

Mathis told Insider that while her kids are loving the arrangement, blending all of the members of the family — including seven cats, five dogs, and four fish tanks — has been an adjustment. 

"I would be lying if I said it was an easy move," she said. But having the kids every day and putting them first "is the best decision we continue to make."

Mathis, a content creator and wedding photographer, first announced that her boyfriend — who requested to be referred to by his initials, TK — would be moving in last month in a TikTok with half a million views captioned "new roomie alert." She said she was sharing to let others know it's possible to find "love after loss." 

TK is still renting his own apartment, Mathis told Insider, but spends the majority of his time with her, and serves as a "stepfather figure" to her three kids. 

Commenters applauded the unconventional, ever-evolving arrangement. "Me with no kids crying happy tears for strangers and the healthy relationship the kids will have with everyone involved," one person wrote.

"This is healing my inner child," another effused.

How the 'team of parents' are able to share responsibilities while setting boundaries

Mathis has worked in tandem with her ex, the former NFL player and entrepreneur Evan Mathis, as well as his wife, sports chiropractor Megan Mathis, to overcommunicate and implement systems and boundaries around the house. 

They keep a binder laying out all of the children's basic needs. At the beginning of the week, Mathis and Megan (whom Mathis called "an angel") plan out dinners, as all six of them sit down to eat as a family most evenings. (TK is less involved with parenting logistics and typically goes to the gym after work, Mathis explained.)

They also keep a giant whiteboard to track monthly goals, and a rotation of parents convene with the children at bedtime to discuss their "rose, bud, and thorn" of the day. 

"Now we have a larger team of parents able to share responsibilities," Evan told Insider. "It's much easier to manifest what we all want out of life when we are collectively co-creating."

The biggest source of conflict, Mathis said, has been disparities in parenting styles. As Evan's been busy launching two businesses, she feels he's assumed more of a "fun dad" role, whereas she's emerged as the responsibility-driven disciplinarian. 

This has led to some "confusion" and "pushback" from the kids — which she, Evan, and Megan have been tackling in group therapy.

"We have the boundary that we will not air our parenting grievances in front of the kids," Evan said, "which helps us avoid undermining each other."

"Every week seems a little easier than the week before," Megan concurred.

'It makes the harder moments worth it'

While many on TikTok have supported Mathis' move, some of the comments have been infuriating, she said, namely the untrue speculation that she's sleeping with her ex. She said it's made her more cautious about what to share.  

Megan, too, isn't accustomed to being on camera, saying she's had to learn to "brush off the criticisms that come from random people on the internet."

But at the end of the day, Mathis is only concerned about the welfare of her girls.  

"They tell us every single day, at least once — all of them — that they're so happy that I've moved in," she said. "It makes the harder moments worth it."