I’m struggling with whether to cut ties with my sister - need guidance

As-salamu alaykum. I’m 16f and feeling really confused. In early September my 18-year-old sister ran away. At first we worried it was for mental health reasons because she had been self-harming, but we later discovered she was trying to fly out to meet an online boyfriend she’d known about three months - someone she met on a suicide forum. She didn’t make the flight, so we managed to bring her home. Before we knew everything, she promised she would stay and accept help to get better. Over October we learned she’d been engaging in sexual activity with a non-Muslim man, using drugs, and likely drinking alcohol. In November we found she was planning to run away again to be with him. My parents met with counsellors and we agreed that if she insists on leaving, he can come to our country so she doesn’t run away - but she mustn’t try to run off. My parents even spoke to him and asked him to consider embracing Islam; he said he would think about it. This isn’t what our family hoped for, but she is very mentally unwell and there’s only so much we can do. Please don’t judge; I know she’s struggling. I’ve been thinking for a while about cutting contact with her once he comes to visit. My parents won’t - she’s still their daughter - but it hurts me to hear my mother crying at night and to see my father staying up worried. I’ve heard my father talking to his doctor about rising blood pressure from stress. I don’t want my parents’ health to suffer because of this. In some of her messages she’s written that she’s “not Muslim” anymore, so I wonder if distancing myself would still be sinful if she doesn’t believe. I don’t want to keep someone in my life who’s causing so much pain, but I also don’t want to disobey Allah (swt). I’d really appreciate advice - from a fiqh or spiritual perspective, and from people who understand how to balance caring for family with protecting your own heart and your parents’ wellbeing.