I'm well aware this is a website for women, but as a guy myself I can say guys can be very immature about things.. So I need a woman's point of view even better a mother's point of view.. I apologize for any inconvenience in advance.

The problem is that I have been dating my g/f for one year and four months.. Her father found out I existed a couple of months ago, I thought that was the least because her mother loved me.. [I believe] her mother is actually one of the main reasons I still see her and am able to talk to her (My g/f).. I havent done anything that I can think of to make her upset or anything of the sort but she has changed and seems distant recently.. And i'm always on my best behavior and never disrespect neither her or her daughter..

What could be the cause of this?

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.