Am I overreacting??? PLS HELP!

When my husband started working at a new place he would talk about this girl quite a bit. Nothing bad but that always stuck in my head. I asked him if she was pretty and he would talk about how this or that was ugly on her. So I was surprised when I found out she was a really pretty girl. This was a year ago. 
I went on his Facebook recently and found out that he looks at her page every single day! I know that she hasn't been working with him for about two months now. I know I'm acting different towards him but I don't want to tell him I've been stalking his Facebook.
I know he loves me and we hardly ever argue. Am I over reacting? What would you do?