How would you feel if your child told you that neither you nor God can protect them

Me and my child were talking about a situation that's going on. I don't want to go into detail but his dad is out of prison. I lost custody of him because I did something dumb. He went to live with his dad and grandmother. A lot of bad things happened. There was a lot of abuse. Then they put him in an all boys Catholic boarding school because of his "behavior issues" and so many bad things happened. I got custody back in November. My ex is trying to take him back. He's 16 so he's old enough to voice his opinion but they are claiming he's mentally ill and a known liar and using what a "therapist" who wasn't a licensed therapist at the school said. So that he's mentally ill and doesn't know what's best for him and I'm bad because of my history. He told me if he has to go back with his dad he's just going to take his life. I said he won't. I'm his mom. I'll protect him. God will protect him. He scoffed at me and said "You can't protect me. "God"(he put God in quotes) can't protect me. Nobody can protect me. I already learned that." So now he doubts me and doubts God and says he's done with that God bullshit and to not ever bring that back up to him. I just don't know what else to say. Nothing I say brings him comfort.

Edit: I did stop bringing up God because he threatened to run away if I continued and not have a relationship with me or his dad. I am trying to respect his boundaries because I know he's serious about running away