Well, you could inquire about it after his date and see if he's fond of her or if he was just interested enough to go for a date and see how it goes. If he didn't ask you instead of her though, chances are that he's not interested in you that way, flirting can be done for fun. And kicking your butt? I would've slapped the bitch...
Why don't you ask him out? Its not the 1800's. Besides, he's been flirting with you and if he isn't interested you could tell him to cut the shit out. By doing that it will free up some potential boyfriends for yourself to date instead of being hung up on him.
I once fell for one of my male friends who was much too old for me and didn't want a romantic relationship with anyone. It was because he valued our friendship to a great extent and it made me feel special, important. When he rejected me, it was hard to deal with, but it was a good lesson to learn and we're still good friends to this day.
Falling for someone just on the basis of attention isn't a good idea.
I would not advise you to not worry about it. I will not tell you as I certainly do not tell everyone else I don't communicate with on this 'site' that bitchy does not merely indicate a mean girl, and it certainly doesn't just mean a tough girl. Not a girl who doesn't take any shit.
I do not think that you should consider asking the two of them how they do not feel about double dating.
Don't worry I have absolutely no encouraging words for you.