"When Justin was in Los Angeles and staying with Jen, he would typically spend most of his time in the guest house of the mansion,," a source told Us Weekly. "He would play music, hang out and, in the final months of their marriage, would end up sleeping in the guest house."
The source said Aniston thought "spending time apart was healthy for any relationship," but Theroux was "concerned" about this theory.
"He just felt more comfortable [in the guest house] than in the main house with Jen," the source told Us Weekly.
According to an insider who spoke with PEOPLE, the two were even divided on which coast to live on. Theroux prefers New York, while Aniston loves Los Angeles. Theroux was also spending more time in the Big Apple during the last months of their relationship.
"Ever since they became serious, the living issue often made them bicker. It was always hard for Jen to understand why Justin didn't like, or at least couldn't learn to like L.A., when she was in L.A.," the source told PEOPLE. "With Jen feeling so strongly about living in L.A. and disliking N.Y.C. so much, she wanted Justin to be happy and that's why she agreed that he should spend so much time in N.Y.C."
Although they were spending time apart, paparazzi photos showed the couple spending time in Mexico for the New Year's holiday. Aniston and Theroux married in 2015, three years after getting engaged.
They reportedly tied the knot at the Bel Air mansion, but TMZ reported that it is possible they were never legally married. The site claims it could not find any record of them getting a marriage license in Los Angeles County. Sources close to Aniston said there has been "talk for a long time" that the couple might never have been legally married. Their statement was noticeably missing references to divorce.
The couple announced their separation on Feb. 15, following several tabloid rumors about their relationship status. They said the break-up happened at the "end of last year" and they wanted to announce it publicly to "reduce any further speculation."
"Normally we would do this privately, but given that the gossip industry cannot resist an opportunity to speculate and invent, we wanted to convey the truth directly," continued the statement. "Whatever else is printed about us that is not directly from us, is someone else's fictional narrative. Above all, we are determined to maintain the deep respect and love that we have for one another."
Aniston and Theroux did not have any children together. This was Theroux's first marriage, and Aniston's second. She was previously married to Brad Pitt.