I [21F] don't know how to end destructive relationship with horrible family

Okay, I really should have posted this long ago. English is not my first language so I apologize for bad grammar/spelling. And also sorry for long post!

In my family there are three kids (I'm the youngest), a crazy mom and a dad that has a new family. My mom [46F] and my sister [26F] are narcissists (I realized this when I read r/raisedbynarcissists and feel incredibly stupid for not realizing this many years ago...). They always think that they are perfect and are always right and I know they are not going to change, mainly because they don't think they have done anything wrong. They are not capable of thinking that they could ever do anything wrong - ever.

I love my brother [24M], he is always trying to calm my mom and my sister down. He is rational and smart but also naive and still think mom and my sister can change. I have not spoken to my father [47M] in a year after he told us that his new girlfriend [29F] was pregnant. He cheated on my mom with another woman a few years ago thus leading to their divorce. My dad and my brother have a family business together.

I live with my amazing boyfriend [20M] on the other side of the world, having the life I always dreamed about. We have been together three years. My mom and my sister hates my boyfriend because he encourage me to do what I want and work with what I love, instead of me doing what they want me to do. They are so sure that the move was his idea and that he "forced" me to come with him. My mom and my sister thinks he's some sort of a master manipulator or something haha. I can assure you, it's the other way around! He has always been there and supported me even though my mom says he is not welcome in her house.

I try to talk to my boyfriend about all of this and he really, really tries to understand but he has a very good relation to his family so he doesn't get how my family can be like this.

Every time my mom/sister/dad writes to me via social media or texts I get a sinking feeling, like I have a stone in my stomach and 90% of the time I start crying. None of them support what I do and are always nagging and telling me to come home and/or break up with my boyfriend. If I don't answer their messages they start calling and they do not stop until I pick up. I am aware that this is not healthy for me and that I should have no contact with them. I have been so sad these past few days and feel physically ill when I think about them. I cannot live like this!

Reddit, how can I get them out of my life without starting a never ending shit storm? I also have to return to this country in a few months and they have my stuff (not that much though).

I am sure they won't think it's my own words and thoughts and blame everything on my boyfriend (he wouldn't even mind that though).

I want to be able to stand up for myself and end this horrible relationship. Can I do anything about my mom/sister/dad without loosing my brother? What can I do?

Tl;dr I want to cut off my family because they're bad for me but don't want to lose my brother.