I'm NC with DF and SM now, which was one of the best decisions I've made. I've experienced;
Not being invited to a wedding,
Watching SC have presents while I stood by and watched, having been given nothing. This was very frequent actually.
Horrible comments from SM about how I believe I'm cleverer, prettier, better at things and more popular that her DC - very odd and went onnfornyears. Anything from swimming to school work!
DF being an excellent GF to the DC ofnatro siblings while ignoring mine.
Unkind remarks from DF presented as constructive criticism using terminology used by SM - her would just regurgitate what she said to him.
Meetings with my DF cut short because she had lost her purse, fallen, had headaches etc and needed him home.
I would point out, Ive had a few SM's. In my experience, they all felt that I was an unfortunate extra AND prioritised their DC to the extent where I was excluded. One was nice once she realised I didn't make a fuss about inequality and accepted my position.
After all these years, I firmly believe that all fault lies with my DF. He could have challenge the behaviours but he always chose not to.