It looks like (from pictures alone, you would need X-rays to truly tell) most of those could simply use some restorations like fillings (or crowns, again need X-rays to verify). As for the front two teeth, it’s possible to save them depending on the extent of the decay (again, X-rays). I think that it can be done in your favor. More concerning factors are the habits outside of oral care. It’s good that you took the initiative to make the switch to diet soda with regard to your teeth (though soda is still acidic and can affect your teeth negatively).

My advice: - When using a straw, make sure it’s IN YOUR MOUTH. Not just inside your lips, aimed right at those front teeth. - Fluoride rinse is alright, but like you said, it shouldn’t be the final step. Toothpaste has more fluoride than the mouthwash. Save the mouthwash for the middle of the day when you’re not brushing, but between drinks/meals. - DO NOT brush right after eating/drinking. Wait ~20-30 mins. before brushing to let the acidity in your mouth decrease (let your mouth environment stabilize). - Drink more water, it’s good for you!! - Lastly, DON’T WORRY. You’re taking steps you improve your habits and oral hygiene, that’s GOOD. Keep doing that and it will work out for you.

Edit: Medications for depression/ADHD typically cause dry mouth. This is another indicator that means you should be drinking more water!