Why would she like him so much?

Ok so my best friend really likes this guy but i have no idea why? She crys about him all the time and cuts his name into her arm....she lies down and sobs about him....but i dnt know why she is so in love with him? He kinda hates her.....they arent close....he says stuff behind her back....he is rude....he makes raisest jokes....is kinda mean to people.......i am kinda his friend so i get why she likes him i like him to as a friend but she is just obsessed and i have no clue why....i have never been in love ....like real love...so maybe i'm missin something but.....i just am seeing if any of you know? should i say anything or???