Why would Selena go out to dinner at the restaurant ACROSS THE STREET from where her ex Justin Bieber lives with his wife Hailey Baldwin?!

Well for one thing, she must love the steaks at Mastro's because she dined at the Malibu location just the night before! Saturday night, she and her friends hit up the Beverly Hills location which is right across the street from the Montage where Justin owns a residence. Granted, he's up in Ontario, Canada with his wife, in their new multi-million dollar mansion, but still!

Selena hid her face as she entered and exited through the restaurant's back door in the alley.

Then on Sunday, Selena was back at it again - lunching with friends at Ernie's Mexican restaurant in North Hollywood. This girl loves to eat out! She and her friends hit the low-key eatery before heading to a Christmast party in the Windsor Square neighborhood of LA. They stayed for hours, leaving around 7:30pm.

We think it's important to note Selena's tee-shirt yesterday ... it's a message tee that says something about taking control of what's occurring in your own life because nobody else will. Hmmm ...

With all this eating out, Selena's been keeping up with her fitness -- hiking every day. She's staying healthy and looking happy ... 2019 promises to be a much better year for Selena if she keeps this up!