(it turned out to be Tonks imitating Sirius in order to make Remus feel better, thus the only reason they're going out is so Tonks can hit dat and so Remus can have Sirius when they're alone)
Yeah, I gather that that is a popular trope. (Although there are so many issues to do with Tonks and Tonks/Remus that annoyed me after HBP, ugh.)
Remus/Sirius will always be one of my favourite pairings, though. To use a DC analogy, they're sorta like the Boostle of Harry Potter!