SO family is rude to me

Ash
A little background my SO and I have known each other since we were about 9. We had about 10 yrs apart due to me changing high school and him traveling. Our families know each other, our dads coached a soccer team together and our moms were friends. His family is completely rude to me though. His brother is dismissive of me why I try to add to conversations and his sister and mom have outright called me names. I'm so tired of it. I told my SO that it is his fault because everytime we argue he runs to them to air our dirty laundry instead of talking to me about it and trying to solve our problems. His mom tried to throw in my face that I don't work. No duh, my SO works 3rd shift and daycare costs over 2 grand a month for both kids and I'm still going to school. Sorry it would cost us money for me to work. I'm so annoyed my SO says it's because I don't speak up more, really?! I have anxiety when I try to add to the conversation and blanatly get dismissed you're right I'm done talking to that person since I obviously don't matter. I wish he would stop running to his family and talk to me about our problems, I feel like it's really hurting us and I don't want to marry him if I'm going to have his side of the family hating me.