I have no memory of them doing things outside of filming in 2015. Gillian spent one evening with Piper at the movies and she had dinner with the guy who dressed Scully and she also said she went to many dinners with Quinto and "pigged out at restaurants". All fan sightings of her were either alone or with friends when she weren't on set with David. I wonder if they were a couple why didn't anyone see them even once. I doubt they did take out for all those months together if they spent time.
We have just a few rumors about them hanging out outside TXF set during all 25 years, anon. I really can’t remember if there was a rumored sighting during s10 filming. I guess not…
The thing is, anon, they both admitted they DO see each other without being spotted. Gillian said they “talked about something during breakfast”, then she said “that’s what we tell people” when David said they only exchange 5 e-mails a year. Gillian also said they share meals together with nobody around and they still have that “chemistry”. Bottom line is, they both know how to hide.