Guys: so i want to break up with my boyfriend...how?

So I have been going out with this guy for awhile...and i just don't like him anymore...he is more obnoxious and snotty and overall rude then before, he treats me like dirt. I was gonna just let him know how i feel but i meat one of his ex's at a party...and she warned me to do it carefully. After she broke up with him he was crushed, he screamed, shouted, and tried to hurt her!! Lucky they were in a publish area so someone calmed him down before he could actually hurt her. After that he called her constantly.... and obsessively he would wait for her to come home from work sitting on her doorstep.Im nervous!! He does have a bit of an anger issue....help! i do feel bad too...so don't think im completely heartless...he just makes me feel like dirt always bossing me around etc.