If it was me I would tell someone like your parents first, you have to. She needs to get therapy or you need to get out of the relationship, this will never go away and will probably get worse and just ask yourself this, what if you ended up having kids together?
I realise you have feelings for here but if she really loves you she will get therapy because if she doesn't she could end up really hurting someone and then what would happen to her. You are stronger than you think and I personally wouldn't want to be in a relationship I could not handle, it's only the rest of your life but your heading for a breakdown and that will take you to a bad place.
Your in a violent relationship and they end in tears.