Space... I just got home and read what is happening. I guess even you sort of expected this to happen. Sorry to hear about it. Just understand that things will be tough for a while but you'll get through it.
If I can bore you with my story... my dad died when I was a kid. Needless to say that this was devastating to my family at the time. I remember going to school and not having a dad. Things were tough for a while. Eventually, my mom got remarried to a great man who adopted me a few years later. Then, after many years of being an intact family again, my parents got a divorce. Actually twice... they got back together and divorced again. Again, the divorce was devastating obviously.
Now, I am (somewhat) grown and as you know a dad myself. As difficult as my experiences were, they taught me a lot about what a father means to his child. I am very close with my dad today.
I tell you this, not to make you feel better, because your short term future is going to be difficult. It is going to be very hard seeing just one of your parents next christmas. But we always think just about the short term. The experiences I went through have made me stronger and taught me about what I can give to my daughter. I don't know if certain things are meant to be for a divine purpose, or they are a natural consequence of random events. But I do know that you will get through this tough time. And when you do, you will be stronger for it.
It is a fact that without some bitterness, you couldn't taste the sweet. Without the ugliness, you wouldn't know beauty when you see it. I know this sounds a little corney but it's true. In your life, you will see divorce, death, pain, etc. at times. These things are unavoidable. But these things can make us better. You cannot do anything about this turn your life is going to take, except decide how to react to it. There are 2 things that you can control in life... your character and your strength. Be strong and maybe in time you'll see that the toughest times in your life will help you in some way... or help your sister... or maybe even your future child.