Boyfriend tweeted another girl was pretty, and tagged her in it.?

I have no idea if I am over reacting, but I don’t have a twitter, and my boyfriend of 9months does. He tweeted today to this girl that she is pretty. And about a week ago I had another problem. He told me he wasnt friends with his ex on facebook, I know for sure he is!!! Idk why he lied because she is pregnant and engaged. Also, I am friends with a couple of my ex’s on facebook, and he knows this. I was going to keep quiet and monitor his twitter for a while, and see if this behaviour progresses. Is that wrong?