Boyfriend always chatting with other girls on Facebook?

[La Mora]

My boyfriend and I are in a great relationship. We have been together for 9 months now.
However, I noticed that he talks to a lot of girls that he knows in Facebook. He adds them and initiates chats with them on Facebook. He is 24 years old, some of the girls he adds he haven't even seen since high school. He has pretty lengthy conversations with them sometimes even very late at night.
He even added his prom date from high school who he didn't see since they graduated and at one point told her "you were beautiful in prom" and sent her another message saying "miss your face dude" which she didn't reply to. She sings and has her little band and suddenly he's like "I will write a song for you to sing", and says things like "we should get together and play music someday" (he plays the guitar).
All the girls he chats with are coincidentally good looking too. Not that I feel threatened by them or anything because I know I am good looking my self, but I just find it weird that he only chooses to talk to the girls who are pretty.
In their conversations, it's not just "hey long time, how have you been doing, glad you're ok" kind of thing. They are lengthy conversations with a lot of questions.
I am annoyed by the fact that he always hits up girls. I am sure if I did the same to him, if I talk to a lot of handsome guys on Facebook, then he would feel concerned too.
I don't know if I am overreacting or not. I am sure he is just being friendly but there's a line that he shouldn't cross and I feel like what he's doing is inappropriate and unfair to me.
What is your opinion? And how do you think I should confront him?
Note: I found out about those conversations when he gave his laptop to me to use it. I always noticed when I look at his screen when he's using it that he always has fb chat boxes with girls and so I decided to check for myself. I know it's not ok to snoop and what I did is wrong, but this is what I found and I'm really worried.

[Alii]

Does he do the same with guys, too?
If not, yeah that is wierd and you're not overreacting.

I think you should calmly confront him and ask him why he's doing this. Then tell him how you feel about it, and see if he's understanding or not. If it gets any worse, I would be dumping him.