The 28-year-old actor, who has confirmed earlier he is in touch with former co-star, stays at her place very often, reported Hollywood Life.
"Rob doesn't have his own place in LA. When he is in town, he sometimes stays at the Chateau Marmont and very often at Kristen's when she's out of town," a source said.
"This gives him the chance to hang out with Bear and Bernie," the source added.
Bear and Bernie are the two rescue dogs, the couple shared when they dated. They now live full-time at Stewart's house.
"Rob and Kristen aren't romantic or anything, but they are still really close and would do anything for each other," the source said.