My ex is abusing me all the time..why!!?

hi, my ex and i broke up like 2months ago now. ever since he has been horrible to me, he will drive past and call me names and give me the finger, he done a burnout on my lawn once and sent me abusive msg. to none of these have i reacted because i dont think he is worth the time to msg back and react too. but i want to know why he hates me for no reason, i didnt cheat on him or anything..why do you think hes doing it.