My GF and I have been together for 7 years. During this 7 year stretch, we've been in different cities for almost 3 years.
After we had been together 2.5 years, I went to University in Kelowna, and she remained in Red Deer to finish her schooling. This lasted for 16 months (2 sets of 8 months a pop). We spent summers together.
Immediately following my university graduation, I had a job offer in Calgary and she was unable to land a position in Calgary. We saw each other every weekend, alternating who drove to see who. We did this for a year.
Now, we've been living together again for a year and things are going well.
The only issue that's stemmed from living apart for so long is pushing back marriage. We've both wanted to "get to know each other" again.