I keep having nightmares

I keep having nightmares that my fiancé is cheating on me. I know he’s not. We are together everyday, we have each others phone password, & social media passwords. Occasionally I will go through his phone.. and everything is the same.. he does not have any female contacts besides family. Same with me I don’t have any guy contacts.. we are all about each other, we aren’t moved out yet.. but we see each other every day after we get off work. He’s never brought up another girl.. like only the first time we started to talk and that was when we was telling each other our past like normal. We have blocked guys and girls who we used to talk and who we dated so they don’t try to ruin what we have. (which they wouldn’t) but I don’t know why I keep having these nightmares? Like twice a week.. maybe a little more. I honestly over think every morning I wake up and feel sick to my stomach... does anyone know what this means?? Is it normal.. is it not... we’ve been together for almost 2 years this June