Kourtney Kardashian & Justin Bieber Playing House As Scott Disick Spirals

Kourtney Kardashian and Justin Bieber's relationship continues to heat up and an insider exclusively revealed to RadarOnline.com that the sexy twosome are already co-habitating!

"They even have matching toothbrushes at each other's houses," said the source. "They're totally inseparable and people are beginning to wonder if it's the real deal."

As RadarOnline.com reported, Kardashian, 37, and 23-year-old Bieber have been spotted going out together whenever they get the chance, including a February visit to a Los Angeles church. And now that Bieber has headed back out on the road for his Purpose tour, they aren't slowing down.

"They're constantly texting and calling when they're apart, but when they're in the same town, she'll usually stay at his place if they go out, or he'll be at hers," said the insider.

As for Kardashian's children with Scott Disick — Mason, 7, Penelope, 4, and 2-year-old Reign — having Bieber around has become a commonplace occurrence.

Said the source, "Her kids have seen Justin there, but he's been around the family for so long it's no big deal."