Justin Bieber feels invigorated by his rumored hookups with reality TV star Kourtney Kardashian.

"He has had a huge ego boost from hooking up with Kourt," a source told People magazine. "It's been going on for a few months. He is used to being swooned by young girls that have nothing else going on. Kourt is a hot mom with a career."

The 21-year-old "Baby" singer and the 36-year-old "Keeping Up With The Kardashians" star were spotted out together at the Nice Guy restaurant in West Hollywood earlier this month, where witnesses described them as being "super touchy feely."

Meanwhile, Kardashian's ex and the father of her three young children, Scott Disick, is rumored to be angered by the relationship, though word is none of it bothers Bieber.

"He more thought, 'Wow,' and couldn't believe that she would go for him,' a source added of Bieber's attitude. "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."

Bieber is already known to be close to the Kardashian family and every indication is that momager Kris Jenner particularly favors him.

"It's just one of those things where it makes Kourtney feel good about herself," a source said. "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."

After more than nine years and three kids, Kardashian and Disick split earlier this summer after he spent the July 4, holiday weekend vacationing with ex-girlfriend Chloe Bartoli in Monaco.

Disick has also since been romantically linked to teenage model Lindsay Vrckovnik.

Bieber, meanwhile, was recently spied on a romantic dinner date with on-again, off-again girlfriend Selena Gomez where he was seen serenading her.