DW's sister and her hub have essentially lived apart for 5-7 years; he works in San Fran metro (and has had extensive pacific travel at times), while she continued to live in midwestern city until kids finished HS (which recently happened, but she still is there). They videochat most nights and see each other at least every other weekend. Relationship seems strong--subject to the caveat that no outsider ever truly knows!
We were apart a lot in our first 8 years, until I took long hiatus from full-time practice. Particularly for first four years after school, we really saw little of each other between her residency and my weeks long business travel. Worked well for us; kept us in the honeymoon phase for years!
Now, however, we greatly prefer having dinner together every night, even if it is just something quick in the hour before going to bed.