I'm not going to make fluffy reassuring noises, because I cannot imagine how you must be feeling.
But I will say that the only way to affect what happens in 20 years is to affect what happens today. What one thing (just 1!) can you do today, that will help you in 20 years?
For me (because I'm thinking I am going to deteriorate over time too) I am thinking of only eating sweet stuff when at home. Since I only buy low carb sweet things to eat at home, that will guarantee I don't eat the bad sweet things...
What about you?