Can I get a restraining order on my friend?

there was this kid i was friends with for the longest time, when he suddenly started becoming obsessed with me, he wanted to hang out all the time till i said i wasnt his friend, ever since then he has been harassing me and spreading slander about me on the internet wherever ive been (i always have the same user name). its really annoying and its been affecting others as well as me. i would like to know if there is a way for this to cease? a restraining order? warning from the police? its creepy how after so many years that he is still harassing me. i think it might be because he is lonely and has no friends so this is his way of... coping? anyway, thank you. btw i am a 19 year old male.