Sorry, this is going to be very long because of the backstory.
I am almost twenty years old, my parents separated and got a divorce when I was 9, just after christmas. The reason for this was my Dad cheating on my Mum. I completely broke down and can barely remember the first year after it happened. He stayed in a relationship with the OW and married her eventually. My sister's and my relationship to her is basically non existent. This has various reasons.
-We knew from the start that she was the OW, this resulted in me panicking at the prospect of meeting her, hiding away in my grandparents' cellar or pretending to be asleep. Seeing and interacting with her made it so real
-My Dad tried to make us all go on holiday together which ended in a company disaster with yelling and a "Us (Sister+Me)vs. Them (Dad+ back then GF), it always felt like we were in their way, not wanted and treated unfairly to which we responded by being stubborn and talking back. After the second disastrous try, he separated the holidays, going on fancy retreats with her and camping with us
-My Dad not officially telling us he was marrying her. We found out from the invites standing around in other relatives' homes. When we asked my father, he got all defensive and claimed he had told us but neither my sister nor I could remember him telling us. Needless to say, we didn't attend the wedding
Now that I am older, I see that I cannot blame her alone, a lot of this is on my father. I have always been a "Daddy's girl" and the separation of my parents and what came after shook me to my core. I was in Therapy for two years. I still love my father very much, despite this stuff he still is an "over average" dad, we often do great things together and he supports me. My "Stepmother" and I haven't talked in years, she is barely there as she lives and works in another town.
Last night I wrote a long message to my dad that I would like to try and "improve" my relationship to his wife (quotation marks because there is barely a relationship there to improve), because I don't want to risk having a good and nurturing relationship to him. It was hard to write this for all the reasons above, after all the times I felt second best/left behind, after all the time that passed and also because my mother would see me basically as a "traitor" if she knew I am reaching out.
Now to my questions:
-What can I do to make his wife not resent me (I know she is unhappy that he is staying where we live because of us)?
-How would you react to this?
-Please just give me any advice/insight from your perspective on how to handle this situation
Thank you all in advance and for reading this mess until the end