Letting emotions out Any advice?

Hello. To begin if you read this thankyou for the time i really appreciate it. In April I found out my mom has been talking to some guy behind my dads back. I havent told anyone this because I feel like its not my place to tell him. Im not too close to him either. I did let my mom know that i didnt like what she was doing respectfully and that she should stop. She has not stopped. She has been going with him everyday. Making him food, buying him clothes, and his kids clothes as well. She still comes home which my dad bought for us to be all okay. Ive been super upset lately crying non atop. My mom left me out of everything. Im always alone at home. My dad works. She leaves to go with the dude and his family. She doesnt make food for me. but she does for them. I can make my own i dont mind but i just miss her. she takes them out. She buys them everything. For their birthdays she gets them gifts and celebrates it. Everything i wished i had woth her she has with them. And im just to the side. When I have doctor appointments she makes me cancel them because she has to go with them. I have no choice i have no one else to take me since like i mentioned my dad goes to work and he does come out late. when i first found out, she took me to eat with “her friends” but it was him and his family. I had no clue until after that. Now i feel all alone and left out. She has even been charging me for little things like a ride to my grandmas or for pads. She doesnt let me work either so i have nothing to buy my own things with. and when my dad gives me money she asks me for it. I dont give it to her tho i buy what i need. I dont see why she has to come to me for money if shes so happy with the other dude rhat can give her some. Overall i just feel very alone and i dont even know wht to do anymore. Any advice? thankyou so much didnt really know what group to post this in.