"After they got back together they were both looking for new places and decided to take the next step in their relationship," a source tells PEOPLE.
Kardashian, 29, and Bush, broke up for a while, but reconciled in September.
Shortly after they reconnected, Kardashian told PEOPLE she was selling her condo. "I love my condo, it's beautiful. However, I feel that it's time to move into a home," she said. "I will miss it, for sure."
At the time, Kardashian didn't say if part of her motivation to move might be so she could find a place that might also accommodate both her and Bush.
As for why they decided to get back together, Kardashian said last month: "We just made the decision that we want to make it work, and the time off was really beneficial for the both of us. I think sometimes people need to take a break just to take time off to see how much they need each other and how much they really are compatible."
TMZ.com first reported that the couple are looking for a house together.