"When he was with Jen they took cars everywhere, which he hated," the source says, adding that Theroux likes to walk or take his bicycle everywhere in the Big Apple. "Even in the cold weather, Justin's been biking everywhere. He's totally back in his element now."
According to the source, the actor has also started to reconnect with his old group of buddies, instead of staying "holed up in his apartment."
"He's making a point to get out every day and to see friends," says the source. "He's been dining with friends regularly."
While he's "obviously going through a lot," the source adds that Theroux is "trying to move on, [and] he's dealing with this breakup in a really healthy way."
Theroux and Aniston announced their separation in a statement released to ET on Feb. 15, where they explained that the decision to call it quits "was mutual and lovingly made at the end of last year. We are two best friends who have decided to part ways as a couple, but look forward to continuing our cherished friendship."
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Justin Theroux Is Turning to Love of Pets After Jen Aniston Split
In the weeks that followed, Theroux was rumored to have sparked a romantic connection with Canadian artist and photographer Petra Collins, but a source told ET that he "is still heartbroken."
Meanwhile, another source told ET that the actor has been relying on his friends to help him cope with the breakup, and that he recently went on a "guy's trip" to France earlier this month.
During his visit to the City of Light, Theroux and his pals attended the Louis Vuitton runway show during Paris Fashion Week, and while his friends were hitting the town and looking to flirt, Theroux was friendly rather than flirty, according to the source.