Here are a few points to consider. It's tough work to lose weight, and is should be approached the same way you do anything that is difficult. You make a plan, you get support, you monitor your progress, and generally you don't expect perfection. Demanding perfection of yourself will probably make you gain more weight. That is the time of the day when you truly need a plan and support.
Exercise really does have something to do with long-term weight maintenance.
Moderate exercise is generally recommended, not because it burns more calories than heavy exercise, but because most people will engage in moderate exercise longer than they will heavy exercise. For example, swimming at a sustained regular, moderate clip will burn more calories than those who race down the pool, and then stand at the end to recover for several minutes, and end up exercising much less than if they had slowed down. If you want to engage in heavy exercise, then build up to it. And it will always be more difficult than moderate exercise, so you have to prepare yourself mentally and physically for it. Notice how many Manhattan residents are slim compared to many other cities in the world.