New research from Duke University says if you spend time around people who have good self-control, then you can expect your own self-control to be good.
And spending time with people who have less self-control will influence you negatively. There is a direct effect of your friend's behavior on your behavior.
In fact, this applies to not only friends, but the people you're around a lot such as coworkers, husband, wife, boyfriend or girlfriend. Surrounding yourself with motivated, healthy people, improves your odds of staying in control.
If you want to help your spouse or partner to lose weight, set a good example by eating healthy and exercising. Odds are they will start doing the same.