How do u write a good love letter to get him back?

i just got out of a relatonship bout 3 months ago.i loved this boy more than life its self! but he dumped me.i was devistated cuz i lost my virginity to him and i thought he jus used me for .so i was furious and sent him some nasty messages.i also admited to cheatin on him.i started rumors about him at skool sayin he has a two inch ..but come to find out he dumped me because i treated him lik crap and he didnt like me smokin cussin and all tht stuff,but i didnt knw tht. so now he has nothin to do with me what so ever cuz i sed all those things.but i didnt knw.i thought he used me.=( so he has a new girlfriend and he says he is fallin for her =( so i want to know how to write a good letter that will touch his heart and to let him know that i am so so sorry....PLEASE HELP ME!