How do I stay positive...

When the doctors are telling me worst news any mother to be can hear ? I’m pregnant with twins (di/di) my baby girl is a whole month behind her brother and they found an abnormal blood flow . Basically her heart is working double to pump blood and only gave me a 50% chance of survival into the next week. They also said since they are di/di, baby boy won’t be effected and I will be carrying my dead baby while he continues to grow . How do I even wrap my head around that? Why does anyone have to go through this ? I’m so heart broken and catch myself crying randomly at work when I see a little girl or hear the name emma(what we want to name her). I talk to my belly hoping she can hear me telling her that mommy needs her to continue being strong because I need both my babies with me. I pretend to be okay and positive when really I want to burst into tears and ask why me ? Why after many years of trying is my baby at risk of leaving me before I get to meet her...

Update; baby girl has passed we got the horrible news 3weeks ago. Thank you all for the kind words and prayers .