Maybe it's got nothing to do with 'blame'. Maybe the girls are hurting emotionally because they've just had a traumatic experience and they just want commiseration. They are probably also feeling a little powerless from suffering a personal violation. I'm sure they would love to punish their attackers, but that's probably not an option, and you just happen to be the misdirected target for their justified anger.
So answer this: have you said sorry? Not "sorry it's all my fault", but "I'm really sorry for what happened to you" and "I'm really sorry I didn't try harder to stop you leaving". Follow those sincere words up with "I really hate that things are bad between us now...I really hope those bastards get what they deserve. But for now, is there anything I can do to help you get over it?" You have now shown them that you are also angry, and shown them who the anger should be directed at.
Then ask them if they want to go get a coffee or icecream or something. You will have tried to repair your friendship. If they choose not to take the opportunity, that's their bad, and they are people you can do without.
So answer this: have you said sorry? Not "sorry it's all my fault", but "I'm really sorry for what happened to you" and "I'm really sorry I didn't try harder to stop you leaving". Follow those sincere words up with "I really hate that things are bad between us now...I really hope those bastards get what they deserve. But for now, is there anything I can do to help you get over it?" You have now shown them that you are also angry, and shown them who the anger should be directed at.
Then ask them if they want to go get a coffee or icecream or something. You will have tried to repair your friendship. If they choose not to take the opportunity, that's their bad, and they are people you can do without.