"He has had a huge ego boost from hooking up with Kourt. It's been going on for a few months," a source tells PEOPLE. "He is used to being swooned by young girls that have nothing else going on. Kourt is a hot mom with a career."
Bieber, 21, and the Keeping Up with the Kardashians star, 36, were "super touchy feely," at the Nice Guy in West Hollywood on Friday, a source previously told PEOPLE.
Kardashian's ex, Scott Disick is upset by the romance, a source has said, but Bieber isn't bothered by talk that he is a rebound for Kardashian.
"He more thought, 'Wow,' and couldn't believe that she would go for him,' the source says. "He brags about how hot she is. He is happy while it lasts. Even if she is using him to get back at Scott, he couldn't care less."
A source previously told PEOPLE that something has been going on between Bieber and Kardashian for months.
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"He's obviously close to the family, and Kris [Jenner] is obsessed with him," the source said. "It's just one of those things where it makes Kourtney feel good about herself. It's not serious at all. This young guy is into her, he thinks she's hot and she's older. She just wants to have fun."
Bieber has palled around with the Kardashian-Jenner family in the past, posting a photo of himself in May swimming in a pool with Kardashian's son Mason, 6.
"Mason is as cool as a fan," he captioned the photo.
The singer also helped celebrate Kendall Jenner's birthday with her and her family at The Nice Guy last month. He was spotted partying with Kendall, 20, on Tuesday.