How do you maintain a friendship with an ex? Take advice from Selena Gomez, who went through a very public breakup with beau Justin Bieber and has kept things friendly.

"He and I have had such a history together and I'll always care about him and protect him if anybody tries to be mean," Gomez said today on "Good Morning America."

The " Come and Get It" singer split with Bieber, 19, in late 2012 after dating for almost two years, but the two have seemingly stayed close. Bieber posted a picture of the couple on Instagram earlier this month, sparking speculation that the pop stars' on-and-off again relationship might be heating up. (Gomez has said the two are no longer dating and Bieber's rep has declined to comment on his personal life to ABC News.)

See Justin Bieber's Rough Year Post Selena Breakup

It's been a busy week for Gomez, who turned 21 on July 22, and got the best birthday present ever when her debut solo album, "Stars Dance," shot straight to No. 1 on the charts.

"I don't think I can celebrate any better than releasing my fourth album, having 'Come and Get It,' and start my tour," Gomez said. "It's been crazy…I'm playing hard and working hard."

Gomez took time out of her work schedule to celebrate the milestone birthday Monday over private dinner at Bagatelle in West Hollywood with family and 20 friends.

The food, the guests, oh my! Click here to read more about Selena's birthday bash

The singer said she's enjoying being a 21-year-old, but at the same time wants to keep reaching new heights in her career.

"I'm having a great time and get to be with my friends and family and just enjoy it every now and then," she said. "My music is doing really well, so I'm just focusing on my work. I feel like the moment I'm not working I get bored and then I go crazy. I'm going to keep going."

And going she will. Gomez's world tour kicks off Aug. 14 in Vancouver and goes throughout Canada, Europe and Russia, before ending in the U.S. on Nov. 27 in St. Louis.