I’m so sorry to read this. My son sounds just like your brother, but he is only 21. My husband/ his father, died 2 and a half years ago ( my sons problems go back to when he was 13, so not a result of this) and as a now single parent, I am determined that if something happens to me, my daughter ( 23) will not have to take on the burden of a life she did not chose/ or should be responsible for.
I understand your feeling that you see him as a young boy….. my daughter has dealt with it by saying that this person isn’t really her brother, and her real her brother was “ swapped in the night” when he was 13 …… and to be honest, I feel the same.
I don’t know the person he is now, nor do I like him.
We will always love the person we knew, and he was.
I am hypocritical to say this ( because I don’t practise what I preach) but walk away.
You have to look after yourself and your children.
If there is one thing I am ingraining in my daughter, it’s that she is NOT his mother, and is NOT responsible for him.
You have only one life – and it’s yours to live.
Sending you love and strength x