Will I ever get over it?

My husband and I have been together for 9 years, married for 1. I love him dearly, I can't imagine life without him and I know he feels the same. However, back in the first year of our relationship (he was 18 and we were long distance) there was a night he cheated on me with his ex. It's been so long, and I thought I was past it but I still think about it sometimes. He is working late tonight, and on one hand I know he's at work. But on the other I can't help but think what if he's not actually working but with someone. Am I crazy? Why can't I get over this already? We are very happily married, but I feel like my insecurities will hurt us😢 am I the only one who feels this way?