Hi.
The best way to stick with it is to figure out what caused you to go off last time(s), and change things. Is it because someone else's junk food is tempting you? Make them get rid of it. Were you unprepared at school/work? Try to do more do-ahead cooking and preparing. Is someone in your life being unsupportive? Speak up about it.
Most people think that all you're doing here is adjusting what you eat. What surprised me the most about eating this way is how I needed to change
everything: when and how I shop, how I spend time in the kitchen, my routines when eating out or barhopping with friends, my thinking patterns (the biggest one) ... be prepared for that.
Nitrates, from what I understand, are carcinogenic.
A bit won't hurt you, but plain meats are generally better. Pork rinds, cheese, etc are fine.
I would skip the American cheese, though... go for the real thing. And make sure you're eating veggies! They're mandatory. Enjoy them with your favorite salad dressing/dip. Three cheese ranch is my fave.
Feel free to tell us more about yourself and your lifestyle, and/or start a journal here. We could give you more specific feedback and advice.