My ex is taking me to court for our 4 yr old son?

ive already gotton a lawyer and we are going to court but im scared. Im scared that him and his god awful gf are going take ny baby from me and i just dont think i can handle that. He is a firefighter and just bought a mortgage over two hours from where we used to live. His girlfriend that he has only been with for a few months is watching my son while its his time to have him and shes been tellin him to call her mom. This pissed me off. She is very overbearing and weird and for some reason wants my son for herfelf. She has a 5 year old daughter and they are gettin private investigators to follow me, give me drug tests, and all sort of things. Im not working at the moment but im about to start school full time to be a RN. I left hom about 3 years ago and because of this gf that he has hes taking me to court and tring to get me to pay child support. Ever since we have broken up we have shared time with our son. We have both been in his life the whole time. Im a good mother and dont want my child to be taken from me. Im scared to death. I live with my sister and its a nice house. What do i do? Any advice is appreciated/ Thanks.