Ugh i want to move out. Vent 😈😠😬

Seems like my mom uses whatever excuse to fight n argue with me I'm almost 26 and she still wants to treat me like a lol girl..... She got upset because my son came to her crying that my fiance got mad at him becuz my son bit him. So my son comes to her crying that he hit him in the face when all he did was tap him in the mouth.... She tells me that I'm a piece of shit because I can't defend my son.... That I lied to her then she wants to tell me to leave with my fiancé but I cannot take my son ugh hello I have every right he's mine!!!! So I told her I just got home and your already arguing with me like really... And so I walk offf and I say I'm not going to argue with you and she says exactly.... Then she all like I'm gonna put you on blast on fb see what your friends have to say..... I'm so pissed Idk what to do the only reason I stick around is because she has health problems and also takes care of my 75 yo grandfather!!!! ADVICE PLZ.....