A playful combination of the names, Finn and Millie. It is a ship name given by fans for the teen actors, Finn Wolfhard and Millie Bobby Brown; who each played a key role in the show “Stranger Things.” It started off just when the first season aired and when their characters El (Millie) And Mike (Finn) had their first kiss. It was seen by some fans (mostly all the st fandom) that the two interacted well together in interviews, etc, like dancing at the premiere together, Millie calling him her ‘boyfriend on set’ and saying she ‘fell in love with his soul’.... this made fans to romantically fantasize about them as a couple.
Fillie depression is when you Look at Millie Bobby Brown and Finn Wolfhard having “moments” together. These “moments” include non stop glancing at each other, Heart eyes, hugs, and the blushing and giggling while talking about The Mileven kiss ( On the show Stranger Things). Signs of having Fillie depression are watching fillie edits all day, internal crying, and constantly talking about Fillie with your friends and how it may have been real.