Every marriage is different so I'll just speak for me. If my wife & I were together 24/7, we'd probably wouldn't be very happy together. We are two different people who have enough different interest that if we didn't let each other go every now and then to do our own thing, we probably wouldn't grow very much as individuals. Sure it puts a strain on things at time, but it can actually strengthen things as well. Its really hard for me when my wife goes of on her retreats but it wouldn’t be right for me to hold her back from her passion just as it wouldn't be right for her holding me back from mine. Leaving my wife and kids behind for 3 weeks of backpacking was a tough choice for both me and my wife. But having that time away from each other actually helped us appreciate each other even more. As for the kids, that was a tough one as well. Yes, I missed and worried about the kids, and they missed and worried about me, but isn't that one of the tougher lessons in life we all need from time to time to develop at least some kind of independence. Obviously 3-6 months would be a lot harder, but we all have to live out our dreams if possible and if that means hiking 3000 miles to do it, one should try to find a way. A supporting spouse is part of a marriage that gets swept aside way to often. Some would call it “give and take”, or “give and receive”, why not just call it “letting each other fly”.
And then there's the reunions, the joy of rediscovering each other, the reminders of why we are together and why we need our space and to respect the space of others.

P.S. Having a dozen roses delivered to my wife and kids was very well received. And finding a few letters hidden deep in my pack was very well worth the added weight. Ok, so I cried..