Am I right to feel betrayed by my friends?

Well 2 of the girls came round just now. I asked if they wanted to ditch me again before I began yelling. But they just came and waited for it. Seems they were expecting the shouting. I did lay into them for being crappy friends and leaving the 2 of us behind. Leaving the girl to deal with me in her drunken state, when really she was entitled to be pampered for the whole day and night. After that I calmed down and listened to them explain.

Ywiss you were right. They were told by the other 2 girls that I was being irresponsible and drinking. Even though they knew I don't drink when I drive, in their drunken states they weren't sure what to believe. But when it became obvious they wouldn't have had a lift home with me, they went in the other girl's car. These 2 are quite upset that such a thing happened, made them feel worse when I told them to cancel all the extra plans we had made until my leaving do. But I'm going to remain good friends with them. They are genuinely sorry.

From all the chats I've had with the birthday girl and these 2, I've realised those other 3 are utter bitches. I hate the thought of breaking off this friendship but more and more things being revealed is showing them in an extremely poor view.

Thanks everyone for your help.