Hi Gemma, welcome to PsychCentral.
I am sorry to read that you are grieving so much not only for yourself but for your mother. Unfortunately your mother was so young not only when she met your father and began having a relationship with him, but also she was very young when she married him as well. Your mother never had a chance to actually learn how to live on her own either which is one of the reasons she stayed in an abusive relationship. Also, unfortunately, we are what we know and your mother only knows how to live in and abusive relationship even though she is unhappy. Also there is a syndrome that women, even children can devlop where they give into and even protect their abusers called stockholmes syndrome.
It's good that you have gotten away from this environment, and even though your mother is still dealing with it, I am sure a big part of her is glad to see that you have found your way away from it where you now have a chance to learn how to live on your own and hopefully when you choose a partner you will make sure this partner is not abusive.
It would be very helpful to you if you found a support group or therapist that you could spend time with that can help you grieve and also heal from being exposed to such an unhappy environment growing up.