Background
My dad has had a girlfriend for 8 years now. She's 37, my father 45, I'm 25. We are French. I was 17 when they started dating. Naturally, I was very happy for him. After 6 months, she moved in. She seemed to be nice and everything was going great.
With time, I started to see that she was kind of a control freak. Everything my dad does was never good enough and she would systematically redo what he did. Then, she started with me. For example, my dad and I have RLS and if we shook our legs while eating, she would be mad. Or when we were talking, she complained that we were too noisy for her to write a text.
I started to be very uncomfortable at home and I locked myself in my room most of the day, playing video games. One day, my dad kicked me out of the house, thinking I was a video game addict. After 3 months, we got in touch and the problem was solved, without really talking about it.
After those events, I moved out in my own house and got a job, so everything was great.
I'm totally independent as I left the family house 5 years ago. I now live with my boyfriend 120 miles away from my father. I'm not sure I'm able to talk to him in private because as I said, she's always on his back, reading texts, intercepting phone calls from me.
The argument
In June, my dad, my step-mother, my boyfriend and I went to a music festival. Even though she hated the type of music, she wanted to come rather than be away from my dad for one week.
The second day, she had a tearful, dramatic argument with my father over a road trip issue. While she was outside, my dad told me something like "She must question herself over time, everyone turning their back to her". So I thought he might be aware of the problem.
On Sunday, she stared at me and said "You think I'm unbearable huh?" out of nowhere. I said "Yes", knowing that if I lied, she was going to scream at me anyway (clearly, she wanted to argue). She started to scream and berate me. I just smiled even though I was very angry. My dad was there, impassive.
Later, I messaged my dad and we argued. I finally told him all the things I have in my heart about her. He told me to grow up (what?). I explained I only spoke out of respect for him and his love, and I have never been mean.
We decided to talk about it later, but she refused to let us talk face to face, insisted on being there, and finally called me a coward when I left. She also told me to never set foot in "her" house.
Problem
Since then, I have not heard from my dad, even though I've messaged him a couple times about some family news. My father and I were always very close, but I think he is blinded by love and it's isolating him from everyone he loves. Unfortunately, they are getting married in 7 months (and my father always hated marriage).
Question: How can I get my father back / to see what sort of person his fiancée really is?