Is it normal to be worried about this?

I was on my computer and went to search for something when the history pulled up a Facebook message with a girls name that I have had issues with in the past. I was curious seeing as how we do not communicate at all. I clicked on it to find it directed me to my boyfriends account (he was still logged in from the last time) and there were a few messages from him to her saying he thought she was pretty and he wanted to chat. I was upset until I saw these were about three years ago. We were still dating, but I brushed it aside. Now...I know I shouldn't have, but I saw another girl and the message started with: "Hey beautiful." So...I clicked on it and started to read. Mostly it was him saying she looked like some porno star and told her how pretty she was and a bunch of other stuff...all of this was from January of this year. We've been together for five years and we even have a beautiful little girl together. I feel awful that I did look at his messages, but at the same time he shouldn't be telling ANY girl that he thinks they're beautiful and calling them pet names. My question...should I be worried and should I confront him?