how to get over a breakup ...

so my ex of 2 years and 8 months broke up with me last week ... it’s been the hardest days of my life ! not to long before he broke up with me he swore we were going to get married and have so many kids etc etc (we’re 18 btw) and since the day he broke up with me he’s been talking not stop shit about me ... about how I’m annoying and fat and how he didn’t like me and it hurts so much because i thought everything was going good and then he goes off and talks about me and UGH how do i get him off my mind