My step son is living with us

I have a step son, he turned 15 two nights ago. That's also when he moved in. Me and my step son didn't get along in the beginning. His I'm bad mouthed me all the time and told him he doesn't have to respect me. His mom is awful and lives disgusting and has put credit cards in her sons name, bills in his name, when he is an adult his credit is gonna be shit. I tried to love him and show him love but he would call me a whore, a bitch, a cunt. He stole from me because his mom asked him to and through all that I never once said he couldn't come back. That is my husband's son, when I married him, I took in his son as my own too. We did have a fight because his dad said this behavior had to stop and he said he doesn't want to see us anymore because he has a great mom and I'm an ugly bitch. That was 7 months ago. Two nights ago he calls me. He's asking where his dad is because he's not answering. I said he's at work and most likely won't even see his phone until 2am. He said okay nvm and hung up. Something told me to call back. So I did and asked was he okay. He said yes and I asked where he was. He said downtown. It was 11 at night. Basically for his 15th birth is mom lied and said they were gonna do something and waited until around 9 and dropped him off at the courthouse and said she isn't happy with her life and is leaving to be with someone who makes the her happy but he doesn't like kids and she needs to put herself first for once and left him at the courthouse on his birthday. I drove to pick him up and he was quiet. I bought him a cupcake for his birthday but he didn't eat it. Next day my husband called his mom and she said the exact same thing he told me. So we have to go to court to get him off child support and her on it. My step son speaks to his dad sometimes but avoids me completely. He was out there for 2 hours before he called me. He mainly hides up in the attic until bedtime reading or drawing, but just keeps to himself completely