There's a boy.

Very aloof. What other way is there to be? Never to pressed or impressed, but appreciative of beauty or his idea of it. He acts interested but just doesn't have the mental energy or stimuli to go through with pursuit.
There's a girl, real chill until the prospect of love arises. What other way is there to be? Very picky about who gets her time, her mind, and her behind (so to speak). But when she finds one, she wants it to work. Badly.
Boy sees Girl day 1: Boy offers brief pleasantries to Girl (she reciprocates) but is content to let her walk away. Boy sees Girl day 2: Boy offers brief pleasantries once again. Girl's interest is piqued because she has noticed Boy before and it seems she is now getting her time in the spotlight. That suits her well. Boy is still content to let Girl walk away but Girl figures this is what it will just be. Nothing wrong with being pleasant. Boy sees Girl day 3: boy offers brief pleasantries. Boy sees Girl day 3 part 2: Boy introduces himself and exchanges more than pleasantries but contact info with Girl. Jackpot! Girl thinks. Girl is wrong.