Moving in with GF and not wanting to leave my mom

Hello guys,

I'm a 21 years old student and live 300kms away from my GF right now.
There are a lot of constellations in my current situation and I will try to display them correctly.
My GF of 2 months asked me to move in with her and her 4years old son because else she wouldn't have seen a future with us together. I didn't want to lose her so I just said yes and only think of the consequences now. One of those consequences is living 600kms away from my mom which seems selfish of me right now but I don't want that. On top of that I haven't told my mom that I'm bisexual and it's hard for me to tell her and I don't want to tell her I'm just living with a friend in another city that is 600kms away from your place. I want to support my mom while living my own life and I don't feel like I can do that when I'm 600kms away from her. I know that this is selfish of me.
I've been studying almost 2 years now in a city that is 500kms away from my hometown and that was OK because I knew it was just going to be temporary but moving in with my GF is actually a life changing decision that I made way too spontanously.
I don't feel like I can talk with my GF about this problem because she will be just thinking that I dont want to move in with her and break up with me but I do.

How do I compromise this? What do you think?

 

I've talked with some people including my best friends about it and they all agreed I shouldn't do it. Especially because we've been together only for 2 months. I would be throwing away my ambitions for a girl. And if my GF loved me she would understand this. I will talk to her, maybe I will post here what happened after that