This is true. It's so much easier when you have actual and not just mental support from your partner. Last year I kept using long working hours as an excuse for gaining weight. Although I work in a gym and have a free access to all the activities, I barely ever worked out. I would say to myself I'll just take care of my diet. Often when I came from work I found my husband eating pizza or cookies and I swallowed my words and the cookies all at once. He was becoming chubbier too. Then for the New Year's (cliché, i know) we agreed we'll start going to the gym together and we'll take care of what we eat. On the days when I was lazy he pushed me to go with him. At first, it felt horrible. Now the workout doesn't feel like a chore anymore and we're both so much fitter. We don't eat junk because we simply don't buy it. He also went from smoking 2 packs a day to quitting and I'm really proud of him. There's a lot you can do for each other to improve lives together. Keep it up.
The way you put this made me laugh :)
I think helping each other be better should be a basic part of every relationship. It doesn't end at physical but, it is a good place to start because it is a keystone habit that supports many other things like, quitting smoking.