I don’t get it?

My ex boyfriend and I went out for a year and we broke up in April 2018. I was upset and he kept on ‘trying’ to make me jealous in May, June and July with this other girl he thinks is ‘PENG’ and they’re sorta ‘linking’. But during the holidays in August, I had a whole month recovering and getting over him. And it worked. I don’t think about him as much or anything. I was happy to get back to school. It’s fucking September and still today, my ex makes fun of me and spreads shitty rumours about me and it annoys me. He says that me and this kid in our year are going out and that I like him because we talk? Like wtf? And then he really hurt my feelings by telling my BEST FRIEND to tell me that he told her to tell me that I smell. And he got his friends to agree. I was hurt and sad. I was expecting my best friend to back me up but no. Why is my ex still trying to me make me jealous and being so rude to me? :’(