Bfs mom is a monster and bf doesn’t stick up for me

I don’t know what to do, my boyfriends mother attacks me all the time for no reason at all. She hates me because my boyfriends two younger sisters aged 15 & 17 get along with me really well. She has attacked me 3 times calling me a bitch and disrespecting me like crazy. My boyfriend never sticks up for me and tells me to keep my mouth shut because that’s his mom and I need to be respectful. Why do I need to be respectful when she’s not respectful to me? Anyways, fast forward to last week. Her and my bf get into a fight and I don’t say anything but go to his little sisters room and then we leave the house to the front yard so we don’t hear her yelling. She then threatens to call the cops on me for making a joke two months ago on getting the younger sister a fake id to go out with me for my birthday. She literally says I’m calling the cops on you and I still don’t say a thing and keep my mouth shut. Then, I tell my bf you say something or I will. So he tells her to stop. We go back into the house and she’s giving me the nastiest look. We decide to leave and she does not even try to make eye contact with me so I say bye and walk out the door bc I’m mad. She then tells the sister to text me to say not to ever go back to the house because I am a bitch and disrespectful for saying bye the way I did. I had enough at this point and this is what I texted her.

My boyfriend has a whole arguement with me about texting her and saying bye disrespectfully bc it’s her house but I was trying to explain I acted like that bc his mother pushed me to my limits. First by threatening the cops on me and then calling me a bitch? What pisses me off the most is the fact that he literally went home and acted like normal with her. Like if you love someone and your mom acted disrespectful to your partner you would be the least mad at your mother right? No they’re literally like best friends he hasn’t even talked to her about the way she acted but gave me a whole talk about the way I acted. It’s been a week. It makes my blood boil that he talks to her and jokes with her like nothing. That’s evident that he doesn’t clearly care about me right?