Why does Peeta fall for Katniss?

title says it i’m reading the books for the first time and i guess I’m having a hard time understanding WHY Peeta develops a crush on Katniss and why he peruses it for so long.

Like i get why she likes him. it’s Peeta. but in terms of character traits what, aside from physical appearance, causes him to develop and then PASSIONATELY pursue that crush?