They're rarely non-magical though -- well, granted, femme's definitely is, but that's a rarity, I think. I mean, generally, the very few we've got, they seem to be (more often than not, because yeah, there are definitely some that are completely non-magical, but more often than not) about one of them being sick of his life, deciding to open a café in the Muggle world (while still being a wizard), running into the other one in the Muggle world (generally Draco, who's been exiled after the war or something, etc.)

I'd link you more but... afraid it's not my favourite trope either :( I've read a few more over the years, but those are really the only ones I ever saved.