If eating right is what's hard for you make cooking meals and eating meals more enjoyable. Ask the FI to help you chop up veggies for the week or try a new recipe together. When was the last time you busted out the nice plates and did a romantic dinner? Try new veggies or styles of cooking. Also this time of year is a great time to go to farmers markets where the veggies and produce are going to be ultra fresh and organic. Nothing gets me more excited to cook when I know I'm shopping locally and about to eat some delish organic veggies/produce.
If working out is your issues, which lets face it which one of us hasn't wanted to just curl up on the couch and never move but that's neither here nor there, find an activity that you don't just like but LOVE. I'm not a big runner. In fact you could say we don't really get along but I know that it's necessary to maintain good health. So I compromise by going for hikes or running around, playing football with the FI. Also, I joined a HOT yoga studio. I don't know what part of the world your all in but Core Power Yoga has studios nation wide and offers a free week of yoga to their new clients. I absolutely LOVE LOVE LOVE Core Power Yoga http://www.corepoweryoga.com/. They aren't your typical studio. They're upbeat, youthful and fun. They have classes for just about everyone. What I love is you really get a good workout blasting calories but also you sweat out toxins in your body plus you get to take a moment out of your day to just breathe and center yourself!
Anyways, point being is like ChocoTaco said. This should be a life style change. Something that you can continue after the walk down the aisle! But it sounds like you're on the right track with getting a trainer. I'm at the 9 month mark for getting married and I def want to tighten and tone up a bit. Good luck to all you lovely 2013 brides!!