Credit: Getty Images

Perhaps having Justin Bieber as your "boyfriend" isn't so great after all.

An insider tells Star magazine that Selena Gomez finally decided to end things with the Biebs after he got high and hooked up with a 22-year-old nursing student on December 21.

Justin and his buddy Lil Twist apparently met up with the nursing student, Milyn "Mimi" Jenson, at the Beverly Hills Four Seasons.

To see pics of Mimi, click here.

“They all went to buy weed at a smoke shop on Olympic Blvd. in Hollywood,” says the source. “Then, they got food at McDonald’s and went back to the hotel."

Back at the hotel, the three of them reportedly smoked pot and drank a cough syrup-based concoction called "sizzurp." Classy! They ended up back at Justin's mansion, where he discussed his love for tattoos and Xanax.

Justin held Mimi's hand while he showed her around his backyard, and he apparently was acting very romantic — and very stoned. Then, he and Mimi ended up back in his bedroom, which is where things got interesting.

Credit: Getty Images

“Justin surprised her by saying, ‘I want to know if you taste good,'" reveals the source. "He started kissing her cheek and ear and neck and then her whole body." At that point, Justin took off her clothes and "engaged in sexual activity with her." Wow.

Apparently, Justin stayed fully clothed the entire time and wouldn't go further with Mimi, even though she wanted to. In fact, the source says Justin didn't even kiss her on the lips.

“He seemed out of it, and even though he didn’t ask Mimi to leave, she decided she should go,” the source continues.

So we're not sure if we can fully believe this story, but if this is true, we can see why Selena got fed up with their relationship!

We also now know that Justin apparently takes his ladies to McDonald's. Quite the big spender.

Source: Star Magazine via Radar OnlineHollywood Life