What the hell is this persons problem?

So i used to sit next to this guy and at first he just kept saying "I hate you." So one day I just said "Aw, I love you too!" so then he kept saying "i love you" then it changed to hate and then he kept calling me a skank. So i called him a BEEP and he found the name really funny so it kinda stuck and we kept calling each other that (we still do). At one point we got on really well and spoke to each other loads! But he calls me really REALLY mean things and has started calling me titless! HUMPH. He says it in front of his friends and when its just us! I used to think "Aw, thats sweet. Maybe he likes me and is just shy?" but after like a year i thought "Shut up you, irritating BEEP" And it's gotten worse recently! Does he hate me or like me? Once we get past the swearing we can talk for a little while but then he starts being mean again! Even when I ignore him he still swears at me!! DOES he hate me or is he just doing it for attention or just for a laugh in front of his mates? Either ways its annoying me and i need to know whether I should just tell him to f*ck off!? Should i just be nice back?