I’m in need of advice.

I am in the state of Texas and plan on staying it Texas; but my question is, if I were to leave the house I am currently at take a bus to my childhood home and leave my children with their father for a bit would I lose my right and have to fight for custody? I need to know asap. I only say that I’m going to leave my children behind bc their father will not let me use his vehicle, and I have no one else in the are that would help me. With how crazy the world is today I will not be taking them in the bus if I do leave.