You're right. The behaviors you have now and the behaviors you need for a healthy, active, trim lifestyle have a wide canyon between them.
When you can't see the forest for the trees, you get a saw and start on the first tree.
but I don't know how to stop.
I don't think I've actually stopped very much, what I did was something else instead. If someone told me that I was forbidden to have another drive-thru meal, my mind would go into rebellion and I'd be sabotaging my own effort relatively soon. But in 266 days today, my drive-thru appearances are now very rare and when I do them, they're totally within my weight-loss goals.
So don't forbid yourself -- replace your poorer behaviors with better behaviors.
The first step in my losing 100 lbs. was awareness. Awareness was the first step to seeing the changes that I wanted to make and I started making them a few at a time.
http://redd.it/2z4e9c
MyFitnessPal is a great tool for calorie counting. To start, commit to use it for a week -- every meal and snack, every condiment and drink -- a week's log complete in the foods and accurate in the measurements. This is not easy, it will take 15-20 minutes per meal and you'll still be vague on whether you're using it exactly right. Just do your best. It's a learning curve. The second week gets easier and more accurate. By the second month, it takes 5 minutes a day.
Print out your log from the website every week and review your meals. See which choices are putting you off of your goals. Visualize what you will do differently next time: less food in that portion, or cooked/prepared differently, or using a different food choice in that meal.
Keep using MFP and reviewing your logs for ideas and inspiration. You'll soon be regularly hitting your goals and the weight will be coming off at a decent rate (1-2 pounds a week on average).
My plan:
Everything else I did stems from 3 three. No large list of rules, and while I can safely say that I've changed a lot of behaviors, I did it in a way where I can say that my life remained my life -- I wasn't trying to follow someone else's weird diet plan that may not fit my life now or in the future. Most importantly, I know what I'm doing after I lose this final 10 pounds -- more of this. Because this "new me" is very compatible with me, I can keep doing it to keep the weight off and make this weight change a permanent one.