As usual, there’s no picture, and it’s only assumptions. We know for a fact they both were in California, and mostly Los Angeles over the summer, at the same time, in July and early August. We know Gillian spent her birthday in Vancouver, though, because she was spotted there the day of her birthday. We know she spent it with her kids, at least. We assume David left LA at this period, but it’s only based on the fact that he left his dog to Nancy Collini who always keeps Brick when David is out of town (for example, she had him a few days ago when he left for San Diego), and maybe there was a sighting of David in Vancouver the day of Gillian’s birthday (or the day before, I can’t remember exactly).
If you’re looking for chronology, I made a timeline of everything that happened between them in 2016, including sightings and rumors. It’s here.