Are They Just Assholes Or Am I Over-Sensitive?

I used to think that when you were friends with someone, there is a line you should never cross. Some people are just sensitive about certain things, and one should not go there out of respect for one another.

It seems like some of the people I've chosen to be friends over the last two years seem to think it's okay to take little jabs at my esteem. I don't know why I chose to be friends with such spiteful people, but I intend to fix that. Quickly.

Example: I've told a friend at work that I liked PG. Now this, of course, was in confidence, but I also told him because he tends to get a little too "friendly" with women at work and makes sexual comments and stuff. This doesn't bother me, nor does it seem to bother them. It's that he's making them at her that bothers me. While I'm in the room.

Now I realize a few things here:
1.) In lieu of everything, PG isn't my girl. I realize that this is the important thing to remember.
2.) That is part of his accepted behavior at work. I've heard how women think he's "harmless," or it's "just Him," etc. I won't go into detail about it, but it's beyond the usual flirty, double-meaning/innuendo banter. No groping, but definitely touching.
3.) It might be that I'm jealous.
4.) Or that I find it to be a slap in the face to me.

I have approached said friend about his behavior, but he has either chalked it up to, "Oh, well, PG and I have an 'understanding,'" or "That's just who I am." Then he would dodge the subject by talking about something they shared about me. Like his behavior is a small price to pay for the "inside information" he can get to tell me. Or, he's just laughed it off.

This is the problem that I see: YOU'RE FUCKING COCK-BLOCKING ME, ASSHOLE!!!

Case in point. Another girl at work, with whom he does those same "things" to, has decided to ask him out. Now this girl has a boyfriend. We'll just say that I don't think she's asking him out for a cup of coffee. And I think a lot of it has to do with his so-called "behavior."

Personally, I don't do those things because it's gotten me in trouble before. Almost-getting-fired-in-trouble. I learned my lesson years ago: It's just better not to go there. Sure, you'll find someone you like and the two of you will hit it off. But do that stuff outside of work. Or at least when no one is around.

Anyway, I started thinking about this only because the other day it happened that he made a comment about her ass while I was in the room. She blushed, called him an Ass, laughed, and left. I tried to block it out, but after they both left I started seeing red. Did he just make a pass at her? In front of me?!? I've seen him do other things before. He's grabbed her to tickle her. Smelled her hair. It's like he's marking her as territory. I just see a huge dog peeing all over the woods. Mine! Mine! Mine! I think that's why it's pissing me off so much.

A part of me says to just toughen up. Things will play out the way they're supposed to. On the one hand, it only matters whether or not PG and I end up together. On the other, if it doesn't happen, it just wasn't meant to be.

But in either case, I'll have to be careful from now on. He's proven to me that he isn't really my friend. And I think that's really the point in all of this.