How can i show my ex that i've moved on and that he made a mistake?

He said i was 'the best thing that ever happened to him' and that i was 'the love of his life', then he ended our relationship for cowardly reasons and because he couldn't handle how serious things were getting, i was really upset about it and now it's been 2 months and i feel really optimistic and ambitious again (myself again) and i'm moving to the netherlands in september. How can i show my ex that i've moved forward with my life and that he's made a mistake? he was pretty immature after the breakup, said things about me behind my back and said that he needed to start to 'audition the ladies', he tried to make me really jealous i however never stooped and stayed grounded! Tips please, thankyou!