La minette et le loup - The kitty and the wolf

Prologue

She was lying unconscious in the shower cabinet when I found her, I started screaming, crying. Seeing her like this made my heart shatter into thousand pieces.
"Call the ambulance!", I yelled to my youngest sister who was crying too. My parents woke up from our voices and my mum started crying immediatly.
"My daughter, my lovely daughter, she's dead, my beloved daughter is dead...". She was screaming like an insane. Only then I noticed that her wrist was slit open, her grey pullover wet and soaked in blood. I don't know what happened then, I only remember fragments, but somehow we all managed to get her out, change her clothes and wake her up. She was extremely quiet, saying that it wasn't that bad. "Read my farewell letter", she told me. "It's on the laptop."
I couldn't read the letter because the emergency doctor came. They bandaged her cut and took her with them. My mum went with them, we - my youngest sister, my dad, my older brother and me - remained at home.
When she was in the hospital, waiting to be operated, she wrote me.
"Hey Sam! Did you read the letter???"
"Mika is that you?"
"Did you read it???"
"No I couldn't yet, should I?"
"Don't, I want to write with you now. If I died today, would you have fulfilled my last wish of breaking up with that guy who is a stranger and return to your family?"
"Hey sweetie, I'm not gone so why should I return? I'm still here"
"No sis, your heart belongs to this boy. Can you leave him? For me? Would my death have gone in vain?"
"Please give me some time to think, I'll give you my answer after your operation"
"Fine, I want answers then"
I lay down on my bed, sunken in my thoughts. Am I able to leave him? Can I do this for my sister? I was crying. "My decisions almost killed my sister", I whispered. 
I loved them both. Him and my sister. I would die for both of them. How should I decide for one?