Saw disturbing messages on boyfriends Facebook, what do I do?

[Sarah]

Hi,

I Hope someone can help or at least lend some opinions about this... I am so confused and upset....

I have never, ever expected him to act like this ! He is not that sort of person he is shy and always has been since we first met and still is today, he is also very sweet, affectionate and caring this is why I am so confused.

I was at my mans house last night, he was constantly messaging on his phone, on Facebook ever since I walked through the door. Two hours later I was getting slightly fed up.
He went upstairs for about 5 minutes to check something out. He had left his phone face up on the table with his messages open... I was sat at the table anyway.
I saw he was talking to his friend but below was a strange message from him to a girl saying: "what do you look for in a guy? X" automatically I thought WTF?!?!

I opened it (yes) and I began reading the rest, judge me but I was on a mission by this point...
The messages read thing like:
-Move to (the town where he lives) and He can meet up with her.
-I will come and see you (wink face)
-you have a nice figure
-calling her Hun and babe
-telling her to ask him questions so she can get to know him better (after she had said u can stay if She knows him better)
-saying he will Move to her area
-said if he stays at her house he will sleep in her room if she doesn't mind (?!?!)
-Desperate for her to move to our town and for her to let him stay (me and my man live separately trying to save for a house! And she rents so she lives on her own)
-he was constantly trying to get an answer out of her things like : ??????!!!!!!???
A lot of smiley winky flirty faces. Pathetic I know but, really?

The thing that annoys me there was no retaliation on her part.
Maybe I am in the wrong but Obviously this is going to raise suspicions... Is this normal behaviour of a boyfriend of three years? Am I over thinking ?

... But I do need advise on what to do. I trusted this man with my life and I have been nothing but faithful towards him.
Any opinions welcome, go for it.... Please!

Thanks