Is it normal?

I have a bf but I’ve recently found myself always staring at girls body’s and thinking every girl is so pretty. I don’t know if it’s normal or if someone’s gone through it. I’m pretty insecure about my body and i just think their bodies are so nice with their curves. I just think it’s really bad that I do it. I look at a girl and think to myself that they’re so pretty and I can’t help it. I don’t think I’m attracted to them tho. I could never imagine myself in a relationship with a girl. Help? I know this probably isn’t the right group to post it in.