A week after returning from our honeymoon, my husband was accepted for his PhD in Montreal. I couldn't go with him, but it was an amazing opportunity with a prestigious researcher in his field. We spent the first two years of our marriage living across the country from one another. We tried to bring him home ever 6 weeks or so, but it was hard, particularly as we had just gotten married.
He is home now after cutting his PhD short (at least the time he was in Montreal) to be with me as I care for my mum during the end stage of cancer. He came home the day we found out.
EDIT: In the 10 years before we got married, we did spend time apart, too. I went to Europe for a month with a girl friend, and he's gone to several scientific conferences. Even after life settles down, I'll continue to have a life outside my marriage. I think it's healthy!