Friend has cancer

Hi everyone 

I'm posting here because I'm struggling to know where to turn. This might be a long post so please bare with me.

My best friend and the person I am closest to in my life has recently been diagnosed with stage 2 bowel cancer. She's in hospital currently as she had her bowel resection surgery yesterday where they found that the cancer has spread to her liver. 

I feel so afraid of what could happen. Our relationship is complicated by the fact we both live with significant mental health struggles and are both in supported living placements. I also come from a nursing background although not currently working. 

I feel like I have to keep it together all of the time for her because if I don't she won't have her treatment. She tried to abscond from hospital today and has been pulling tubes out all day despite 1 to 1 care. She trusts me and she listens to me even when she's struggling with paranoia when she won't listen to most other people so I feel like I have to be there for her constantly despite the toll it's taking on my mental health. 

I guess I'm just asking for advice on how to be there for her without making myself unwell. I feel selfish even posting this because I know it's so much worse for her than it is for me but I feel so helpless.

Thanks if you made it to the end of this post.