I need to know what is really going on?!?

Me and my ex departed ways after i got upset and wrote him a letter, i was extremely embarrassed and hurt so i took it out in a written letter to him. note: i did not disrespect his "manhood" . after that day, i left him ALONE . i did not talk to him , about him, comment about him when he was brought up or ANYTHING . because i believed itll be best to leave him alone. its been a month since we've talked - and when my friends bring me up to him he bad mouths me alllll the time , and i mean nothin positive , then he always says he doesn`t want anything to do with me. it hurts but then at the same time its annoyin and fustrating . my thing is if u dont have anything positive to say , leave me alone , and give me the same respect ive given you. i already passed the guilt and regret of writing the letter and dealt with it. but it seems he hasnt . im 17 and hes 18, and im really annoyed about this. i havent approached him about any of this , and i need to know why a guy would act like this , im tired of hearing amateur answers