Cheated now being Harassed

Yes! I screwed up, I know I did and I pay for it every single day. I feel like scum. Like trash. So please I dont need that right now. 
But I need some help. 
The guy i cheated with has decided after a year to turn my life upside down....he posted about me on a public sight "trying to get in touch with me" and now not only has he tuined my relationship but he has continued to email me, and its begining to worry/scare me/frustrate me. He says if I dont talk to him hes just going to post more. Im so lost at what to do, but hes making me really just want to end it all. 
I don't understand why someone would do something like this! When there were never any feelings or anything there! 
So much lead to the cheating theres too much background to even explain 😥