1) Stop feeling guilty. It doesn't help. People who morally work themselves up about their weight and shape tend to just make things harder on themselves, which makes the process a whole lot less enjoyable, which makes them more likely lapse into bad habits, and then they're more likely to say: "Well, I made a slightly counterproductive decision, I may as well throw in the towel, binge and quit altogether."
2) Focus first on eating healthy. Choose whole grains instead of processed sugars (they're better for your insides, and they're more filling for the same amount of energy, which means you don't feel the need to eat as much, which makes it easier to lose weight), eat lots of vegetables, if you want something sweet go for solid fruit (pro tip: go 2 weeks without anything sweet and a red apple will taste like candy, or at least that's my unintentional experience), eat meat and eggs and nuts, if you're thirsty drink water or unflavoured milk. Don't get too zealous about it -- you can eat chocolate and fast food, it's just that fresh food is generally more filling and nutritious for the same amount of energy, making it easier to consume fewer calories overall. You call it "junk food," but that's moralising it. From now on, it's "sanity food." If 95% of what you eat is wholesome, giving yourself the other 5% for sanity is relatively harmless. Just note the difference between 95:5 vs 30:70, and you'll probably be alright.
3) Once you've got 2 down, maintain that style of eating until it's a habit. Once you're comfortable eating a balanced diet, assess how it's affecting your weight/size/body composition. If you're shrinking, continue eating exactly as you are. If not, reduce portion sizes by 10%.
4) Exercise isn't exactly required for weight loss, however increased activity does increase energy expenditure. This includes both exercise and incidental activity (everything else you do). As far as exercise goes, cardio is often touted as the best thing for weight loss. It isn't. Cardio isn't bad, but it isn't magical, either. You can burn just as much energy doing resistance training, and resistance training does have better implications for metabolism and body composition (ie you may lose the same amount of weight either way, but with resistance training a higher percentage of that weight lost is likely to be actual fat -- if you're going to lose 20lb (just to throw a number out there), I assume you'd prefer to lose 20lb of fat than 10lb of fat and 10lb of something else).