Hi Drew,
I am a little confused, who was it that abused you? Was it your Dad’s wife, or her daughter? I’m sorry for any confusion on my part, I just want to make sure I am understanding correctly.
TYour Father States he wants a better relationship with you. A better relationship includes trust, openness and honesty. You have to be willing to trust him to be honest and open with him and vice versa in a loving way. If there is no trust, or you are afraid to approach someone on an issue regarding physical abuse without fear of shame, their can be no relationship. I would open up to your father about everything. If he gets defensive or angry, just say “I’m sorry, I thought you wanted a better relationship with me, I was hoping we could have a trusting and loving conversation about something so upsetting for me”. If he gets angry or defensive, he does not want a “better relationship” keep us posted.