OP this is awful of your family!! No wonder you havent been able to forgive yourself what many/most people would consider a very human response to the violence directed at you by the real villain in this situation - your violent abusive ex!
I don't think there will be many reading this who won't assume that your family was also abusive and controlling to have this dreadful response - and for you to have internalised it so deeply and so immediately.
The fact that you called the police on yourself shows that you already had more than your fair share of guilt and shame which could be easily triggered.
Most people would have been deeply grateful that nothing happened, and they would have forgiven themselves for an act undertaken in extremity. But you did, because you had already been used to being made to feel guilty and ashamed.
I'm really surprised that the police charged you actually, although maybe they had no choice.
Now though, you have to forgive yourself. You need therapy to do so because it will involve looking at your terrible family and working through what they have done to you.
I'm so sorry you went through this and have carried this burden all this time - honestly, it's making me feel quite emotional.