false assumptions? please no.

I don't know what to say.
Strange for a blog, right?
But it's a complicated thing and yes, I'm gonna talk about very personal stuff here, that's what a diary is for and it's my blog so I can do whatever the heck I want, right?
Moving on.

I have this friend and he's my best guy-friend and we've been really close for a year now and everything was fine until now, it seems.
Here's the backround-story. He's the best friend of a friend of mine and he brought him to a party and we met there. We met 2 times after that at other soccer-related parties, exchanged e-mail adresses and instant messenger numbers and started talking online. Soon it became a habit to spent at least an hour talking to each other everyday. There were interesting and dumb times, times when we didn't have anything to talk about, times where we felt like we couldn't stop talking. Everything a friendship has. Except that we haven't seen each other again for a year. Just those 3 parties and the rest was only online talking.
Last friday, exactly a week ago, we've met again at a party. I didn't know he was coming, hence me wearing something very low cut. I like teasing stranges with the things I wear, but I alwys try to be careful around my male friends. Not that I'm full of myself, but they've told me that it gives them a hard time when I wear something sexy and that it's difficult for them to keep their eyes off of my cleavage.
However, I behaved I was nice I tried hiding it by sitting awkwardly, but I don't think it helped...
Since then, my best friend has been behaving a little weird. Many of his comments, now, have poorly hidden double meanings and just everything feels weird! Also, we're skyping a lot these days, which means we can see each other and I can watch his reactions and his facial expressions.
I'm getting a little uncomfortable, but not for me, but for him. He has a girlfriend, whom I don't know personally. I have met her once or twice, but I have never talked to her, I think. Anyway, he always tells me that he loves her and that she's the one, but he still keeps on making those comments!
Guys, is it fun for you to play around with other girls even if you say that you've already found the right girl to be with?
I don't get y'all.
If someone could explain to me, please, why the boy keeps on doing that?!
Also, I can't say that I don't like the comments/compliments he makes. But I smell big touble running and soon crashing into this situation... I don't know.
It kind of scares me that his girlfriend might think something wrong about me, that I'm stealing him from her, that she just makes false assumptions in general.
I don't want yer boy, he's a friend and it has not once crossed my mind that he might be more. It's only for his comments that I am now thinking about this, because I'm afraid that HE might not only think of me as a friend anymore.
I have no problem with men objectifying me.
However, I DO have a big problem when my friends do that, because I don't objectify my friends.
Oh, and I've told the man that I am not "single" for him. To him, I am "taken" and I will always be. He knows that. I don't know if he has already forgotten, but I did tell him that.
Basically, I want to know what's on his mind, that's all.
Any help would be appreciated.