My best friend's mom hates me and im losing her because of it?

This girl has been my best friend for 4 years now. We've gone through so much stuff together and I would die without her. But her mom... let's just say she has made my life a living hell (I'll call her mom X and my bff Y). X has cut off Y's friendship with a mutual best friend of ours (I'll call her Z). She said Z is a slut because ONE freaking time Z wore a tshirt with the sleeves cut off and you could see her sports bra. X is SUPER uptight about boys and dating and stuff. You litteraly have to be a perfect angel for her to like you. Well now X is starting to pull me and Y apart because my parents let me do whatever i want (not true), i've had a boyfriend, and i've liked 3 guys in the time me and Y have been friends. The first guy she was talking about was when I was 13!! and i didnt like anyone else for 2 years after that. I had a bf for 3 weeks (the stupidest thing i have ever done), and now i like this incredable guy. He's my best guy friend and has been for about 2 years. We're going to prom together, and X really doesn't like that!! I have no idea what to do!! I'm losing Y over a guy, and yet I know if it wasn't that it'd be something else. Her mom reads all the text messeges between us, deleting them doesn't help because she has this website thing that she can read them off of :\ I'm dying inside right now. How can I keep from losing my best friend????