Can you really move on ?

Ladies! Let me give you a little back story before I ask my question.

My fiancé and I have been together coming up on 5 years. We are both 19 turning 20 and we’ve been together since our freshman year of high school. When we were 14, I moved to another state because my step dad had a job opportunity that he had to take to support us. We tried to do the long distance but we were really not loyal. We never “slept” around but we were flirting with others, texting others, snap chatting. I’ve never done anything physical but he called me one day crying and told me got head from another girl. I felt heart broken, and so devastated . We broke up because of obvious reasons. I ended up moving back home and we decided to meet up (same month he cheated) he admitted for the whole year I lived in a diff state he was flirting with others, and he told me he regrets it all and didn’t realize how much he loves me. I was really hurt because he told me everything he did. After months of working together, we stayed together and been together since. Sometimes I still have trust issues because of it and I honestly think about the times he has done me wrong.. he hasn’t cheated ever since and has been nothing but good to me. But lately ive been seeing everyone say “once a cheater always a cheater” “he’ll never be a good guy if he cheated” and I’ve been stressing and having anxiety. Do you think I should stress ? Will I ever be able to get over the pain I felt 5 years ago? When I was doing the same thing to him? I need advice. I’ll admit for months I won’t think about it at all, but then I’ll have dreams about him cheating or I’ll see a girl he used to flirt with and I’ll get angry. I’m so happy with him and I need to know if me stressing is dumb or do I have a valid reason to stress and worry.