My sister has been in a relationship with a Muslim guy for 4 years and my parents are still unaware of this.

I(20f) have a sister(24f) who has been in a 4 year relationship with a Muslim guy. She has been hiding this from my parents. My parents are unaware of this, and I’m starting to feel like I’m in trouble for hiding this from them. She keeps pressuring me to relocate to India so she can be alone with him. I don’t like the idea of her living with someone who is not her husband. I don’t want to hide this any longer because I feel guilty and horrible. I’ve told her to tell my parents because if they find out later, it’ll be worse, but she won’t. I’m scared that if I tell them, she won’t forgive me, but I can’t keep this from them anymore. Everyone is unhappy in our house due to this. What should I do? It is a responsibility to keep our house happy, especially when our elders are there but, it is my responsibility to protect my sister.