My last GFs went Michelle - Jessica - Michelle (again). The "Jessica incident" was due to university.
Basically, I was going out with Michelle, but between my uni courses, her uni courses, my placements, her placements, and work; we started seeing less and less of each other. Michelle suggested Jessica and I should hang out, as neither of us had a lot of friends, and we both liked the same movies etc. I eventually cheated (kiss) on Michelle, but by that point it was pretty amicable and there wasn't to many hurt feelings.
Jessica and I went out for about a year, but Jessica knew I still loved Michelle; and behind my back was talking to Michelle about it, me etc. One day out of the blue she 'dumped' me, but had arranged for Michelle and I to get back together.
Yes, the whole thing was a bit weird!
My point is yes, not seeing them for a while can be a concern, and can defiantly strain a relationship. However, if you love your BF, you'd be surprised what you can make work.