I want to run!

I've come to the point in my relationship where my boyfriend and I are completely comfortable with one another. The butterflies are gone. The newness of the relationship is gone.
I've always struggled at this stage. I associate the butterflies with being in love. So now that they're gone, I'm always questioning whether or not I'm in love and my instinct is to run. Mind you, he's literally everything I've ever wanted in someone and we have no issues at all. Someone please tell me this is normal and I need to calm the hell down. Lol.