This is the 11856th most frequent Korean word.
널
"널" can mean "you" (informal pronoun) or "plank/board" depending on context.
In this sentence, '널' is the shortened form of '너를', which means 'you' in the object form.
널 기다리고 있었어.
I was waiting for you.
Here, '널' again represents '너를', indicating that 'you' is the object of liking.
널 좋아하는 이유가 있어.
There is a reason I like you.
In this case, '널' is '너를', showing that 'you' are the recipient or benefactor of the preparation.