Well at least ubare about to be 18.sounds like your gf and her family are great people..well after u are an adult stand ur ground.always let ur mom know u do love her.but let her know u are a man that will defend the woman he loves.after u are not there living and u go visit.and lets say ur mom starts on anything with ur girlfriend..nicely say to please dont talk about her..and if she does keep going..just nicely leave..then call or text her let her know u love her but u will not tolerate the woman u love being talked badly about..just tell her let u visit and dont bring her up or everytime u will leave..and commit to this..each time put a little more distance first time maybe a week of ignoring 2nd maybe 2 weeks..and so on..maybe your mom will eventually catch on.
My husbands mom is kinda the dame exact way to me for no reason.my husband doesnt really talk to her much because she likes to control my 34 yr old husband and his kids until me he let her comtrol him and his kid's..she easily manipulated him..stand ur ground now cuz when u have kids it wont end with u..there are some serious mental issues my mother in law is diagnosed with..she makes stuff up on me..i even took a polygraph test 4 times and passed..yes on a talk show too..my husband was a teen who had play in the yard and ldnt go anywhere unless she was there ..ill have to keep up on ur post and let u know more..best of luck