Is it normal to hate her and feel bad about it?

I am so confused over the way I feel about my mother. There are times when I'm so angry at her that I feel like spitting, and boy does she always manage to make me angry! But then I feel heartbroken over the way things are between her and I, to a point where I pity her.
My mom and dad were never married, and neither were they in a relationship when she fell pregnant with me, so my father was never a major part of my life. But my mother has always been what I call "sex-oriented" because she just can't handle being single, even if her 'relationships' only existed in her bedroom. She had so many boyfriends throughout my childhood, and all of them were either drug addicts, alcoholics or paedophiles (sometimes all 3 in one) and each of them fueled her desire to be young again.
I went though hell with her and her abusive boyfriends, putting up with verbal abuse, watching her get beaten up, having to witness her sexual exploits with these men, having these men turn to me...it was more than I could handle. So I left and have been living with other family for four years now (I just turned 18).
The thing is, she has never once apologised for what happened. Its bad enough that she would rather lose her kids than to straighten out her life, and she continued to live with this pig of a man she called her boyfriend for years after I left. That was like a slap in the face. What's worse is, there have been times when she has really battled for money, and (feeling sorry for her) I let her not pay my school fees so that she could sort herself out. But she never thanked me. Ever.
Another thing that has hurt me about my mother, is that she would go to the ends of the earth to keep her horse, that includes going without so that the stable bills can be paid. But why couldn't she do that for me?
For years I have suffered the consequences of HER actions. I'm insecure, I never trust my judgement, I expect the worst out of everyone I meet, I live as the burden to the rest of my family - almost like the charity case. And she just doesn't see how any of this is her fault!
Everything my mother does is to benefit her and her alone.
Recently, she has started living with us because she finally left that man(actually, he left her). And I've seen that my mother has nothing. She lost all her friends, and all her respect because of the things she has done. Without me and my aunt, my mother has nothing and no one. That thought alone is like water thrown onto a fire pit. My anger just dies, and I feel sorry for her.
But within minutes she can make me so angry. I have no respect for her. And it just kills me because there is so much left unsaid. I have tried to talk to her, but it always ends up in a fight. And she's often said I look donw upon her, and that I need to get over the stuff that happened. But I just can't. Is it normal to feel 2 conflicting feelings towards the same person? Pure, hot hatred? Or pity?