How do I deal with a mentally ill family member without being dragged down myself?

It's really hard! With practice you teach yourself to detach, go someplace else emotionally. While they rant you look at them and pay attention to their facial features or a spot on the wall behind them. Like I said really hard but you have to try not to take it in.

Find activities to do together that are enjoyable and not stressful. Find a support group for family, and also encourage your family member who is ill, to seek out support groups, too.

If you are a carer for this person then you need assistance.
If their behaviour is so bad it's either a clinical issue or they are well aware of what they're doing and it's a form of manipulation.
In either case i suspect Respite care is of the urgency and a discussion with a social worker as to future long term care plans and how to implement them is long overdue !
Nobody likes to admit defeat. Especially when caring for one you love. But it does neither of you any good if you just continue the same cycle again and again, with you feeling like you could strangle that person !

Find a support group that deals with caretaker issues. You can share experiences and find out how others cope.

you have to just let it go!!! I know it can be difficult at times but that is about all there is to it. Just always remember "they" are the one's who are mental not yourself.

I'm sorry you have to deal with that . I had a family member like that and I allowed myself to be consumed by that ...never again

Sweetie you just can't ... emotional attachments prevent that . You need help

Self preservation makes it ok to flush toxic people out of your life. Relatives or not.

Sorry you are going through that. 😢

Isn't there help out there for you both? Is this person involved with any Mental Health agencies? Is this going to go on for the rest of your life?

Wow
They'd be better off without you .
Try putting yourself in their shoes it's not a choice .