Will somebody plz help me understand?

ok............theres this girls that just came to my school me and her have been talkin since.... ive been walkin her to cl being late for alot of mine well here is wat gets me i finally go to ask her out but she tells me she doesnt want a boyfriend right now i said ok well the very next day i find out she hooked up with this dude that i cant stand first of all i cant get over why she would lie to me like that second why couldnt she tell me she didnt like me so it wouldnt hurt me so bad? plz tell me how i can get over this the dude knew we was talkin should i beat his *** or wait till football?