I lost 2 stone at 70 and at 75 it has not come back, all the extra weight was put on just before and around the menopause and was intractable until I was 70, when the 5:2 diet came on the scene and worked for me.
I think, and I would not claim to be an expert, that successful weight loss is to do with your attitude to food. Your description of how the constant focus on what can be eaten and exactly how much exercise to take gets you down is probably the clue to unsuccessful weight loss.
What I found helped me was developing an eating and activity pattern that suited me and I enjoyed. I always claim that I have not done a seconds Exercise (the capital letter, government and doctor recommended misery activity) since I left school. However I have always been active. I like walking and go out for a long walk every day and I am generally always up and down and doing stuff in house and garden, I used to do a lot of swimming, things I really enjoyed doing. Do that and forget about Exercise. Find what you like doing and enjoy doing it. Do not measure it or make it a chore.
The same with food. Imagine and plan what you would eat to maintain your weight, without gaining and then find ways of eating and, more importantly, enjoying eating like that. Research recipes, adjust recipes for food you already enjoy so that they are lower in fat and sugar. Get pleasure from the food you eat.
For me, the 5:2 worked, I think because when I started it, I began to research recipes for the 500 calorie days, looking for ideas, picking recipes that included foods I liked, trying new ingredients. I made eating on the '2' days, I cut back as enjoyable as the sensible balanced diet I ate on the other 5 days. I also ate on those two days in a pattern that suited me, which was 2 meals, lunch and supper both the same size, other people cut lunch or only eat once a day.
To sum up. Forget about diets, cutting back, doing Exercise. Instead take pleasure in food and being active, develop a way of eating that suits you and that you really enjoy (the key point) and keeps your weight stable and then, think how to adjust this to lose weight and ENJOY.