Long distance relationship

Hi, so I’ve been wanting to get this off my chest. I’m in a long distance relationship(states away 16+ hr drive) and it’s been over a year. I love him a lot. Whenever we are physically with each other I am the happiest person. We only got to see each other 5 times this year I am getting my period this weekend so I don’t know if the hormones have anything to do with this but I am in college i graduate in May and a few years ago I was good friends with this guy and he ended up liking me and it just never worked out. I see him frequently because we go to school together he has a girlfriend now too. All of a sudden i find myself thinking about him and how cool he is. I feel really guilty about it. I even had a dream about him last night and we were texting and being kind of flirty, I woke up in a panic because I was so upset with myself I would never want to do that to my boyfriend. I would feel very insecure if i knew my boyfriend was having thoughts about other girls. I know i want to be with my boyfriend but i am confused on why i am having these thought about this other guy almost regret. Has this happened to anyone else in a long distance relationship or in general? What’s wrong with me?!