Relationship help, attracted other girls?

Yeah, this is normal. I know how you feel. When you fight with your girlfriend, you start going on the mindset of "What would my relationship be like with her, or her, or her?" It's natural to have these feelings, but you should know that when you and your girlfriend are having a nice time together, you know all those other feelings aren't necessary. But, like I said, it's natural to have these feelings. It just means you're human.