This question has come up loads of times in the message boards of SP. I believe there is no real answer, because staying motivated is a very personal path/battle. Just as there is no miracle pill for weight loss there is no miracle motivation maintainer.
Motivation comes from within, it comes from your soul telling your food addiction to "shut up". Your soul getting to a place where you will not be beaten anymore by something as innocent as food.
My motivation is not a dress, or a swimsuit or wanting to look like a supermodel. My motivation, the "it" that clicked, is wanting to be happy, wanting to have energy, wanting self confidence and wanting to beat my addiction to food.
It will not be easy, but surprisingly it will not be hard. Get yourself into a routine and find balance/moderation in your food intake, not all or nothing. I started with Gillian McKeith's Boot Camp Diet: 2 weeks to a new you. I turned this into 4 weeks. It is pretty hardcore and does make you address so many other things than just food intake. Get your husband involved, we all need to eat healthfully to have a better quality of life.
Good luck and