Is this guy a player?

I think this is a guy who is overly confident. Not arrogant, but overly confident.

But for some reason, he views you differently, and loses the usually cool nerve he has with approaching girls.

I will also offer an alternative. I have known guys that have friends that are girls. They are such good friends with these girls, that they could ask for this kind of favor from them to get the attention of the girl they are interested in. I'm not saying that this is going on in your situation, but it wouldn't surprise me if that's what it turned out to be.

Sounds like he is a genius. He wanted to get your attention and he did it. Still, he was willing to use someone else in the process. Is that the kind of guy you want to be with? If you're ok with how he went about getting your attention then go ahead and go for it. Still, don't be too surprised if he hurts you one day. He has already proved he is willing to use people to get what he wants.

i think this guy probably likes you, but he feels as if you rejected him, when you did not encourage his advances. He wanted to see how you dealt with him parading this other chick around you. He wanted to test your reaction to her. If he puts back after having been flirtatious then he probably does really like you and he is backing up because he realized he may have shown you too much. He is a mind-f#$% and is playing head games, not so much a player. Is he still with this girl? If so leave him alone (he might want his cake and eat it too) if not play his games right back with him and see if you feel he is genuine--if you think he is than sure give it a go. The worse thing that could happen is it did not work out and you move on.
Good luck.