How do i kno if im over my ex?

me and my ex were together for 3 years and we broke up 3 yers ago cuz he cheated on me, and nowim wit my highschool sweet heart again and w been together for 2 years so far and we plan to get married soon, i just keep having dreams of my ex cheating on me overand over so now i think eveyone cheats even tho my fiance now is so diff