i dont understand why also?

after broke up cant be friends?you treat me worse than a stranger..i dont like the feeling that i have now..it feels damn uncomfortable..dont know why.."someone told me that"..why the girl ignored the guy from the day they broke up ..the girl hardly talk to the guy anymore..the love in the heart so fast disappears?i dont know also..i want to know it also..the girl never feel anything when she did that to the guy..i also feel really weird about that..can you tell me?