I fell for you - is the correct translation
The current translation “I like you a whole lot.” works quite well here. I wouldn’t say “I fell for you” works much better, as it seems to imply romantic interest (doesn’t it?).
Feel free to use the report function to bring our attention to sentences like this one. Here, I would probably add “I adore you” as an alternative translation to make this more transparent.
przepaść ‑padnę ‑niesz ‑padł (pf), (impf) przepadać 1] be lost. 2] & za + Instrumental = to be very fond of / enthusiastic about s.o. or s.t.