Tbh I knew a mother like that- her bio son was 5 years old when he caught his dad cheating, he told him mum and never spent the next 20 years blaming him for blowing up the family. He was trapped because his dad ignored him for opening his mum and his mum used to blame him.

If OP takes the kid in she’ll probably blame and resent him and I don’t know what’s worse because his being abused my his dad and I can’t see OP being any better so maybe the best she can do is let him get to 18 and form his own family.

ESH here except the kids, his 14 OP do you know what it probably took him to tell you, knowing the consequences and wrath of his father. YTA but you already know it. His dad is vile