dating my stepbrother

Anonymous bc my friends use this app. So first off, I didn't date my stepbrother.. My mum dated my boyfriends dad, which has pissed me and him off through the roof. I am 22 and I have been dating Josh for two and a half years and throughout this time my mum met Josh's dad and they started dating too without us knowing. Which is obviously disrespectful in itself because she kept it from me. Also, they're engaged. Not married. I am disgusted by this because now I will be regarded as the girl who is dating her step brother. Not the mother who is dating her daughters boyfriend. Also, she stole my thunder pretty much. She got engaged to my partners dad! She should of been waiting for her daughter to be engaged. I know this seems crazy but I'm emotional and sick of it all and I need advice