Thank you for your replies.

I know I can't fix it and I know he has abandonment issues. I'm trying to make sense of it.

My dad remarried and has step children and I sometimes feel 'less than' too, but I know he loves me and I'm happy for him. My mother loves my brother and I equally, but does know me better because I made the effort to 'know' her.

I guess the root of my problem is as sarahsweets says: Is that someone you want to be in a relationship with?

Ending the relationship with him means my mum won't see her grandson.

So I think the best I can do is just put up with it until my mother passes away and that's when I believe things will finally be over with my brother.

It's a shame because I do care about him and I would like things to be different, but I have to accept he will never change. I've accepted my parents won't change, but I struggle to accept that about my brother.

He said he wanted to help and he was a great support through cancer treatment but as soon as the mental health issue came up....he shut down. I guess the root of that issue is whether or not my mother's behaviour is narcissistic or she can't help it 'cause of mental illness. That's important because if someone abandons you as a child it matters to you if they did it to hurt you be ause they didn't care or if they were genuinely so ill they couldn't help it.

My mother believes the past is in the past and it's not fair to resent her for something that happened due to serious illness. It would be like blaming her for getting cancer.