If your g/f's mom has changed towards you, maybe your g/f has discussed some personal things with her that she doesn't like. Have you and your g/f had any recent fights/disagreements? If so, maybe she has vented to her mother and her mom has formed a new opinion of you, instead of just listening to her daughter vent. What does your g/f think is up? Is she worried about the change? Has she talked to her mom about it? A few more specifics might help. I am a mom, and my daughter has a boyfriend too, they are both 19. They fight constantly but have been together for 4 years now. I love him like he was my own son. When they fight I try not to form any bad opinions...in fact, I will listen to both sides and try to give the best advice to either of them with no favoritism.