Oh, OP, don’t be so hard on yourself.
For me, I only got to grips with healthier eating (I didn’t go on a diet) when I decided my body, and me, were worth nurturing and treating well. That healthy eating was an investment in myself.
Even one small change (for me it was butting out unhealthy / excess snacks) can make a significant difference, and a small success made me feel better about myself and therefore motivated to treat my body even better, iyswim.
I lost 3 stone simply by cutting out snacks (except for things like carrot sticks or an apple), having a healthy breakfast that I enjoyed, a balanced and not excessive lunch, and a normal dinner but very sensible on portion control for carbs or anything very fat-rich.
And I aimed for 1lb a week, so progress was slow and steady. And the changes I made were sustainable.
It did take a week (maybe 5 days) for my sugar craving and appetite to reduce. Habit is everything! But once I was in the new habit it was really not that hard.
And don’t be defeated by bad days. So, you ate a multi pack of Twirls (yes, I did that in the middle of a period where I still lost weight overall), so what, don’t beat yourself up, just move on and back to healthier eating or whatever approach suits YOU.
Enjoy your body. When no one is looking jump up and have a bit of a dance to the adverts on TV. Take a short brisk walk. Use lovely body lotion. Every evening list 3 things you achieved, however small.
You aren’t a bad person OP, your focus was elsewhere and weight crept on. No big deal, now you can ease it right back off again.
Good luck!