How can I have a normal life

Hi, my sister's diagnosed with schizophrenia this April and it's getting worse and worse. She was also in a closed psychiatric ward for a few months so that she can find better treatments but it wasn't helpful, so she's staying at my family's house now.

I obviously love her, and she's so kind that all the auditory hallucinations that she's been hearing are about our families' well-being. She's just terrified and anxious when it comes to our health.

She's not even sleeping well ever since she had schizophrenia so she always wakes up in the middle of the night and walks around our house.

My mom is the only one who takes care of her since my dad is busy with work, and I'm going back to school soon. She couldn't sleep well because my sister can't sleep and she's always crying whenever my sister tells her the voices she's heard.

I'm only 20 years old, and I know that I have to be responsible for taking good care of her, but it terrifies me that I have to live with this illness for the rest of my life. I sometimes had to cancel my plans because of my sister(because she can't stay alone at our house), and I can't even talk about my sister to my friends or my boyfriend because I honestly feel a bit ashamed and I just want to hide away from this topic.

My mom always tells me that I have to enjoy my life and she'll take care of her, but it just breaks my heart because she always loved going outside and spending time with her friends.

I always lie to my friends or boyfriend when something happens to my sister, so when I lose contact with them or change our plans, I tell them I was too busy about something else. I know this is no big deal since this is just changing my plans and stuff, but I also feel a bit anxious that I won't be able to do anything because of my current situation. My boyfriend also wants to spend time with my family but I had to hide them from him since we're all sad and depressed now.

I feel like I'm living a lie, and I don't know how to find balance in my life while carrying the responsibility of my sister’s condition. How can I learn to cope with this?