Doing a once-in-a-lifetime hike such as the AT is different from being gone for weeks at a time as a regular thing. There are many more instances where one partner is a work-a-holic and just as distant and unavailable and in this case, it never ends. It is all a matter of balance. If your spouse knew that you were a backpacker when you met, then why would they not encourage that important part of your life? There are times, like when children are little, that you may have to put backpacking on hold, but it is all give and take. Also, it would not be a good idea to go do the AT and put your family in financial risk. I believe the OP was about doing the AT, a one-time goal. You also have to balance the impact of NOT doing the trip- are you going to later resent your spouse or hate yourself? But, the good news is that if you stay healthy and in shape, you can still do the AT in your 50's or 60's, so time is on your side.