My husband moved to America from Mexico. So, that was not away from me, but it was away from his extended family. He did live for 9 months in Bogata, Colombia during our marriage. I saw him about once a month for a long weekend.
My husband’s sister move to the Dominican Republic for a few years right after we got married. She had been living just a few houses down from us. We saw her about twice a year. I would not say we were extremely close, but we did have her very close by, and my husband had been accustomed to going to her for some things. When his car was stolen when we were engaged he called her first, before me. She had been the go to family member for him. She is 7 years older, so she had always kind of watched over him. He seemed to handle it fine though. He never said anything about being stressed out about her moving.
My sister moved to NYC when she was 14 and I was 16. I lived in MD? I only saw her twice a year. When she moved back to MD I moved to MI for college. We talked about once a week, I saw her maybe twice a year, hard to remember. My sister and I were very close growing up and for many years.
Then I moved to FL after college. Moving away was never a very big deal. But, your sister is moving very far away, and basically only one way to get there, flying (or a very long cruise) and so I can see why you will feel the distance more.
The up side is Australia is a fantastic place to visit. She probably will fly home now and then, almost everyone I know who moves countries does. I have a friend right now visiting her family in Russia, she moved to America 7–8 years ago. You both can also meet up in places in between for vacations. Now with skype you will be able to communicate in a way people couldn’t years ago.
Do you both spend a lot of time together now? Face to face in real life? If most of your communication is done online and phone, it won’t be that much different. If you saw each other all the time, then it will be a change for sure.