Hi, I'd like to help you with your question.
What you are feeling is very normal. You are a normal healthy person who feels guilt over someone else's distress, even if that person brought it on themselves.
The phone call from your boyfriend's mother probably added to your guilt. She is asking you to do something about a situation you have no control over. If the police were the ones to charge him, there is nothing you can do about that. His mother may have a co dependent relationship with him. It is common that parents do not want to believe their children can break the law. The parents want to believe that everyone is against their child and their child can do no wrong. This dysfunctional relationship helps continue the adult child's belief they can do anything and should not be blamed for it.
The fight was not your fault. Your boyfriend chose to act out and damage your home and hurt your son. To do nothing would have sent the message to him and to your son that you value your boyfriend more than you value yourself, your home and especially your son. By allowing him to get arrested, you helped show your son their are consequences to breaking the law.
Guilt is meant to tell you that you have done something wrong. But in this case, you did not. You only feel as if you did because you have taken on the responsibility for what he did. What would you do if you had it to do all over again? Would you change what you did? What would be the consequences if you did? Ask yourself these questions. If you would not change the situation, then accept that you did the right thing and move on. Repeat it to yourself as needed until you can let go of your guilt.
You once loved this man. And he may have had qualities you appreciated. But his behavior and lack of control has overrode his good qualities. If he was left to do what he wanted, he may hurt you or your son again. It is hard to think of that. It is easier to remember his good side when he is not there to remind you he has a bad side too, one that is very damaging and hurtful. You have a right to not have to deal with that bad side. And he has a choice as to whether or not he changes. Let him own the responsibility for what he has done. You may find that jail helps him rather than harms him. It may be enough to help him change, for good.
I hope this has helped you,