My best friend stole my guy?

[piano smasher!]

So I have been pursuing this guy for a couple of weeks now. We have gone out to dinner together, to the theatre twice, and done some other fun date type stuff, but its all casual. We go to different colleges, so he took me to see his, and he came to see mine, and we met each other's friends and everything.

So this weekend, we go to a nightclub after a double date with a friend of mine and a guyfriend of hers. But her guyfriend had somewhere to be after dinner so it was just me, my friend, and this guy I like.

We get to the nightclub, and of course my friend and I are dressed up in short dresses and heels and everything. With the way she was dancing and how short her dress was, I could see she wasn't wearing any underwear. I didnt really think anything of it at the moment. She goes commando alot. But when I came back with my round of drinks and saw how she was dancing with him.... Let's just say, he was definitely aware she was going commando as well.

They live on the same line, and I was going the opposite direction, so they rode the train together to get home. I hadn't talked to him for a couple of days, but all of the sudden I log onto facebook and see that the two of them are "in a relationship".... WTF???!!?! How am I supposed to deal with this!?!?