I am sorry about your mum, and the anger she took out on you for so long.

I do think that you have a few things in your favour tho - one is that you are aware of what is happening and you dont want to ever hit a girlfriend. Self awareness is a massive step in the right direction. The other thing is that you were defending yourself from your mum. Its not like you have gone out and hit her first?

I think your mum is a unique situation and I dont have a problem with self-defense, in fact I applaud it in situations like your mum. I dont condone hitting from either sexes, but I do like someone who's been abused to stand up for themselves.

I do think that its time to get away from your mum, spend less time around her so not to give her the opportunity to lose it with you. If she's still hitting you at your age, then you need to get away. Put that together with your own self-awareness and willingness to break the pattern, find ways to make sure you give yourself time to think in heated situations - walk out the room, count to 10, anything for a few moments to assess the situation, and I think you'll be ok.

hugs.