You seriously need to go to prison. You didn't play a part, you were every single part. The reason your step daughter could even have the audacity to make up such a lie is because she couldn't possibly foresee the absurd level of complete distrust of your son, and subsequent absolute over reaction in refusing to post your own freaking son's bail, because you decided he was already guilty.

Look, the justice system just did its job; they arrested your son on accusations YOU brought forward. The school did its job; they expelled the dude who was bad for their PR and wasn't attending because he was in freaking jail. Besides, his parents already decided he was guilty, its only natural for the school to expect him to be guilty as well. His friends never had an obligation to like him before or after the incident; they can decide they don't really want to hang out with him regardless of what they think about the charges. Besides, he's fucking broken emotionally because of what you did to him, not much people would go out of their way to hang out with someone like that. Hell, even your step daughter has less blame than you. As I said earlier, it's almost insane to expect someone to react the way you reacted, and while she's despicable and incredily stupid, you are more so in this situation.

It would be almost wrong of him to forgive you; you having maliciously and systematically destroyed his life. Of course if he wants to, that's his prerogative, but there is literally no way you can fix this, and no way for him to give you a chance. The only way he'll forgive you is through some complete blind love despite anything you have done or could do.