My mom is pregnant and it is not from my DAD!!!!?

so i got home from school today and my mom sits me down in the living room and tells me she is having a baby. I say great mom now i wont be the only child and i asked her wheres dad because i know he would be excited too. she then says well hunny thats why i want to talk to you because your dad and i arent going to be together and he's not going to be apart of the baby's life because he's not the father! I started to cry and say what do you mean? But my mom got up and walked into her room and locked the door! She won't talk to me and my dad keeps coming in and out the house carrying his stuff into a van...please help i dont know what to do, i keep crying and screaming at my mom to open the door but she wont acknowledge me!!!