Congratulations! 55lb is a big chunk of weight to not be carrying around!
It's very true that for weight loss, diet is the single most important variable, but that doesn't mean exercise doesn't matter. The kind of exercise you do matters a lot, too, particularly once you start caring about lean mass vs fat, rather than just the gross scale weight. Cardio has this image as "the way you lose weight", but I think that strength training is vastly superior, overall.
Strength training doesn't have to be ultra time-intensive or strenuous, but it has huge benefits for both health and weight loss; muscle is metabolically-active tissue, taking 6-10 kcal/day/lb to maintain, vs 2-4 kcal/day/lb for fat. This has two implications: first, in a caloric deficit, the body will preferentially catabolize unused muscle tissue over fat, since it's more expensive to maintain, and second, maintaining a greater percentage of your weight as muscle rather than fat increases your daily "just keeping the lights on" caloric expenditure. A caloric deficit with a high-protein diet and even moderate weight training will result in a significantly higher level of retained muscle mass, resulting in more net calories/day burned, even on the days you don't train. Think of it as the difference between active and passive income - the more "passive caloric burn" you can rack up, the easier it is to make progress towards those goals.