Busy schedules and long periods away from one another are reportedly the primary reasons for the split, which happened about a week ago.
Bieber's performance at this week's Victoria's Secret Fashion Show may have pushed the strained relationship to the limit. He reportedly flirted with some of the Angels after the show and saw "The Lion King" on Broadway with Victoria's Secret model Barbara Palvin. On Friday, Gomez tweeted a photo of Bieber and Palvin to her more than 13 million followers with the caption "….." Meanwhile, Palvin tweeted, "hey everyone. please calm down. he is all yours!! :) please :)"
Bieber, 18, and Gomez, 20, confirmed they were a couple in early 2011, though they'd been rumored to be an item for several months beforehand. In an interview last month with Oprah Winfrey, Bieber said, "I don't keep her separate from me because I don't ever want to make her feel like I'm ashamed of her." The interview is set to air Nov. 25 on OWN's "Next Chapter" series.
In an interview featured in the December issue of Glamour, Gomez said she adored Bieber's fans, even those who've expressed jealously about their relationship. "I would never, ever want to disrespect them," she said. "You know, I get it: I was obsessed with Jesse McCartney growing up! He was my world. My high school crush. So I respect it, and if anything, I admire it."
The couple share a dog named Baylor, who they adopted from D'Arcy's Animal Rescue Center in Winnipeg, Canada. Bieber is currently on a world tour to promote his "Believe" album and Gomez recently wrapped production for the Disney Channel's "Wizards of Waverly Place" TV movie.
Representatives for Bieber and Gomez did not immediately respond to ABCNews.com's requests for comment.
ABC News' Danielle Genet contributed reporting.