While working out in any form is much better than being a couch potato, making a change in diet is a major factor in losing weight if that is your goal. One thing I have noticed from watching other people is that they make a major change in their diet which in the beginning works like magic but they have made such a drastic change that is is unsustainable in the long term. Then they slowly revert back to their old eating habits.
You've put your finger on the two hardest things - permanently changing habits of eating and exercising that are decades-old.
For me, extremes are easier than moderation and habits are easier than flexibility.Actually, flexibility comes very easily to me, but I mean that in changing things, I have to forego flexibility.
By extremes, I don't mean telling yourself that you'll work out an hour a day seven days a week or live on stuff you don't like. I mean that you permanently cross certain foods off your menu and treat them as dangerous to your health. You form new habits and discipline yourself long enough that the habit of eating the new foods takes over, like eggs every morning instead of breakfast cereal every morning. I do a lot of simple omelettes now.
You form a new habit of having two snacks a day and they don't come in wrappers or bags, they come from the produce aisle or something like deer jerky or Greek yogurt. Friday night pizza becomes Friday night whatever. McDonald's and Wendy's become Subway. You give yourself no mercy about going in convenience stores.
Tell your wife you really need her not to buy the foods that got you where you were, to please dish up reasonable portions and avoid making meals with grease and heavy sauces like spaghetti and meatballs. if she won't jump on board, and she will probably complain at first, it will be difficult. You might keep a backup meal in the freezer when she makes something you shouldn't eat.
For exercise, set a reasonable workout regimen you can keep because you at least halfway enjoy it. More sports or outdoor activities, less treadmill. Get in the habit of doing it at a certain time of day so your body and mind remind you. It helps if it includes someone else that expects to see you, like a workout partner or running partner or a team of some kind and if it is every weekday before work.
For as long as you need to, you keep a log of calories and exercise. My Fitness Pal is a good app for that but I just use a spreadsheet on my desktop. If you set rewards, make sure they are not things that are temptations like eating whatever you want the last day of the week, but something entirely unrelated and enjoyable like extra $$ in a savings account toward a new rifle.
Attitude - success breeds success, discipline breeds discipline. Enjoy looking better and having more energy, simple food tasting better and being wiser about your health. If others aren't complimenting you, make sure you do. It's not silly. You would compliment your wife if she was losing weight and it's important reinforcement. I don't look in the mirror and tell myself I'm a champion or anything. I don't like puffing myself up. But I do tell myself that I'm looking better and I should.
Don't go back. Buy a new belt and throw out the old one. If it gets tight again, tell yourself it's too bad, you're not buying a bigger size, get back on the wagon or suffer. Make no exceptions for old favorites like donuts or cheesecake. It won't kill you to give some things up when you have good replacements. Remember, you used to date different people before you got married, but now you date the same person every week and hopefully that's working out well.
That's my recipe. If you can do moderation, go for it. But if you need to lose more than 20 lbs. my guess is that you don't do moderation as well as you think.