What is normal?

So my boyfriend and I have been together for 2 years. I love him and we live together. We argue, but no more than the average couple (i think). I'm happy with him and don't have thoughts of breaking up.

Occasionally i'll have thoughts about being single and other men. Is this normal in a relationship? This is my first serious long-term relationship and I'm curious to know of this is a sign that i'm not as happy in my relationship or if it's a normal occurrence for people. It's not a daily thought, maybe a few times a week i'll think about single life or imagine what sex would be like with a different person.

Just want some clarity on my thoughts. Thank you 🥰