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Some background
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I am a guy.

When I was 6 years old, my biological father (an alcoholic) died of some heart condition. My mother, older sister and I moved to my mother's family home with her brother's family. My mother's father found a male widower through family contacts who had recently lost his wife. He had two daughters. One was my age and other was 3 years older than me. The widower and my mother got married in April 2004 and we moved again to his home. Within a week or so of being there, he started yelling at us (my mother, sister and I) for no reason. He would slap me on the face, punch me, scream at me, call me useless even though I slaved myself to make him happy. He would also force my mother for sex, scream at her, make her cry, blame her for any inconvenience he faced. He would also grope my chest and ***, slap my *** PUBLICALLY, laugh at me, humiliate me in front of others. My mother would advice me to keep quiet and take it all because it might stop if we don't fight back. It dawned on me when I was 15 and left my home for high school that he was abusive. I am 23 now and I finally went to the therapist and she said that I have severe major depression and suicidal tendencies.

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Main Issue
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A few days ago, I had a serious argument with my sister. She insisted that I help my father with the business as lockdown is in effect in my country. I, for obvious reasons, did not want that. I was working on my office stuff on my laptop. She then proceeded to yank out my USB mouse. I caught her hand and held it away with force and said, "I will throw your phone in your face". She almost broke my mouse by grabbing it with her other hand and throwing it at the wall. She then left and came back with a plastic bucket that we use in our shower and threw it at me with all her might. She then proceeded to call me ungrateful and started swearing, insulting me. I was still calm. I picked up the bucket and started walking past her to the shower to put it back. Then she called me a Mother****er and I lost my control. I punched her twice (not with all my strength) on her shoulder and she started kicking me. This was the first time in my life that I was fighting back. I was bullied in school for 5+ years and never fought back. The scuffle ended with a small bruise on her leg and full 32 prints of her teeth on my arm where she bit me, and a small head bump where the bucket hit me.

She now thinks that I am an abuser, and says that I should thank her like she's a generous god because she didn't go to the police with domestic violence complaint against me


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Question Time
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My questions:

Was is domestic abuse?
Am I an abuser?
Was she not at fault?
Is it all on me?

I admit that I made a mistake when I punched her shoulder.