I promised my daughter one thing: nothing would change when my new wife and her kids moved in. But less than 24 hours after they arrived, I opened the front door and saw my daughter’s face—and everything stopped.

I’m Johnny, 45, and the most important job I have is being Stephanie’s dad. She lost her mom to cancer a decade ago, and since then, I’ve been her rock.

Stephanie, now 14, has always had one of the two spacious rooms in our home with a private bathroom. Her mom’s curtains still hang over the bay window, and I swore that room—and this house—would always be hers.

So when I got engaged to Ella, who has four kids, I made it clear to Stephanie that nothing would change for her. She was cool with it as long as she kept her room, bathroom, and toaster oven.

Ella, however, wasn’t thrilled. She thought Stephanie’s room should go to her two daughters because “it’s just space math.” I put my foot down. “This is my daughter’s space. It’s not up for negotiation.”

Ella backed off—visibly irritated but silent.

When Ella moved in with her kids, Stephanie tried to be gracious. But Ella immediately began pushing boundaries. That first night, she brought up the room situation again. I reiterated: nothing changes for Stephanie.

I left for a client meeting the next morning. When I got home, I was greeted by the sight of Stephanie on the couch, eyes red and puffy.