Selflessness. Charity. Compassion. Placing the other person's happiness above your own. I'm no expert on how to maintain a happy marriage, irrespective of career. However - and admittedly at the risk of generalising - I think a lot of relationships fail because of a lack of the attributes mentioned above, by one or both parties involved.
I'm extremely lucky that my wife has these attributes by the bucketload. As for me, I'm still working on it. I can say this much: I don't know if I would have had the patience to stick around for so many years and put up with so much crap if the tables were turned. Thankfully, I don't have to consider that scenario. Or maybe I can just attribute it to my mother-in-law of all people (who would have thought?!?) who gave my wife this sage piece of advice just before we got married: if you love your husband, don't make him spend his life working in a miserable job just for the sake of paying the bills, as he'll only end up resenting you for it.
Furthermore, my wife and I, along with our children, are regular church-goers - whenever work permits me to be home on Sundays (which for some reason I manage to pull off quite regularly). Those who know me will have a good laugh that the Bunglerat would ever find himself playing for Team Jesus, but for us it's a natural aspect of our daily lives - as much as breathing air. We don't consider ourselves religious nuts, and we respect other peoples' beliefs enough to not shove it in anyone's faces. As such, I'm certainly not going to say anymore on the subject, except that when you live your life with the knowledge that this entire existence is just a temporary one, a slight detour along the way to something far greater and eternal in nature, well you don't get so hung up on the short-term, small-minded issues of money and career - especially one in aviation. As much as I've invested a significant portion of my life in being a pilot, I know I won't be lying on my deathbed wishing I'd spent more time in the cockpit. Being a pilot is just something I do, it's not who I am as a person - and my wife recognises that fact. So at the end of the day, we somehow manage to make it work.