Ok my girlfriend and me have been arguing for awhile. Mainly because she lied and broke a promise, but I'm willing to work it out with her. Well her mom started to yell at me and now a lot of things are messed up and I was wondering how to deal with her mother. Btw she thickheaded and she doesn't know the whole story

First cool down, and as for your g/f mom? Respect and honor, as she holds all the cards, whether you like what she says or not. Her house, her daughter, her rules period. Never involve her in you ad your g/f's mess. This is a fight you will never win.