Hi @Sister2,
I can relate to what you are saying - I have been a support carer for a family member with a serious mental health issue for more than 20 years. Whilst thankfully my family member is doing a lot better now thanks to a strong professional team and good strategies in place in the beginning it was very difficult for both of us as I was his only support person.
I clearly remember one time when my child was a few months old one of my family member's friend's told me that they needed to end the friendship (between my family member and themselves) as the relationship was becoming too much for them. They asked me if I would I mind keeping an extra eye of my family member as they were concerned as to how my family member was going to respond to the end of the friendship. Maybe I shouldn't have said it but at the time I told them that `I was doing everything in my power to take care of my family member but I also needed to take care of my own family, my infant child, and my own mental health so no I wouldn't be keeping an extra eye on them'. I remember feeling guilty, frustrated and alone but I also began to realise that I can only do so much, be so much, help so much etc. As much as I will always help support my family member I now have boundaries in place for my own well being. Is there other people that could help with your sister such as another family member?
The years of being a support carer has led me to really embrace the idea of putting the oxygen mask on yourself first before you can help anyone else - I really believe you can't give what you don't have. If you haven't already I would encourage your to look into getting some support for yourself to around being a carer - here is a link support for carers.
Sending you understanding and wishing you all the best.
FloatingFeather