She grew into an emotional and physical bully

I've been married over 20 years. After our first child was born my wife used sex as a form of control over me. She rejected 99% of my advances and only allowed it when she got something she wanted. It got worse as the years went on,when I tried to initiate sex,she would assault me in bed. I've been punched,bitten and scratched. I know it sounds disgusting and people will say I should have left years ago,but I stayed to protect my children. She is also an alcoholic with mental health issues- (I didn't know when I first met her) and grew into an emotional and physical bully. It's wasted much of my life but I'm middle aged now with no interest in sex (I think it's psychological after the rejection and being attacked when I wanted sex)- I'm glad I have no interest anymore,it means I don't get frustrated and resentful but Im also sad as I'm still fairly young and good looking. But I've made my choice.