I remember one client who said that one of the hardest things about losing weight is not having support from the family. The family would be eating Cheetos and drinking Kool-Aid, or the spouse would be giving her chocolate and alcohol to show how much he loves her. It's hard to be healthy when everybody around you is not.
But this is my best solution for those of you in this situation: you need to be the example!
So, even if everybody around you is "falling by the wayside," you still need to continue on the right path. Even if nobody supports you, you need to support yourself. Otherwise, your entire life would be based on what OTHER people are doing.
Want to exercise? Then exercise. Want to eat better? Then eat better. Want to think more positively? Then do so. Want a better life? Then go get it. As long as you're being an example, the people around you will catch on and follow.
Sometimes, you need to BE the change if you want to see change in others. If you're waiting for others to support you, then you'll never get the support. You'll continue living in your old ways. But if you decide that THIS DAY you will be the example, then you'll see many great things happen in your life!