Anyone have any tips for writing a short novel-length story centered around an internal conflict? QAQ

If it helps, I'm writing a fanfic about a character who spends almost the entirety of the story living in an unfamiliar + different town and lifestyle to improve himself for his crush. The internal conflict involves how he's trying hard to improve himself while consistently longing to return to his original lifestyle with his crush. Ig you could think of it as something similar to 
•"How much longing should we see snowing down to have the days of spring"
•"How long do I have to wait and how many sleepless nights do I have to spend to see you" and
•"Passing by the edge of cold winter, until the days of the spring, until the days of the flower blossoms, please stay, please stay there a little longer"

(You get a cookie if you know where these came from)

I'm mostly struggling with expanding the storyline without going too off track of the basis I want to stick to: how it feels as though the protagonist is fighting an internal fight alone until the end, how they're truly trying hard (physically + emotionally) and doing everything they could for their crush

Gaaah writing fanfics can be hard X'D

(ofc, if you need them to be able to help, I could give you more specific details-)