Can't Stay Focused. Gaining Weight

I feel your pain

Don't have treats in the house!

Perhaps you need to change your diet ( hate that word) your meals. Most days I feel full and I'm not tempted as a result.

I use heavy kettlebells so I make sure my protein is between 100-130g and find when it's not I'm snacking.

I roast chickpeas in various spices, salt and vinegar and even cinnamon so at least I'm getting protein plus not heading to crappy crisps, I eat a square of 75% chocolate (Lidl) almonds 25g which is about 20 nuts, cottage cheese, protein shake with high protein yogurt I could go on........

Surround yourself with people passionate about health and fitness. If you can't find such people in real life, stay connected with online people here on MFP or elsewhere.
Also, it may help changing your mindset. A diet is supposed to mean eating at a reasonable deficit to lose weight, but many people think they need to eat as little untasty food as possible while doing crazy amounts of cardio. Sure, they'll lose weight at a (dangerous) rate and will claim that they feel just fine. Some people catch themselves in time and switch to good habits to keep off the weight they lost but often, the results of that kind of abuse catches up to them and they tire out, crave old favorites, overeat, and regain.
Depending on your personality/preferences, I also can recommend doing one of two things:
1) Slowly wean yourself off of foods that you tend to overeat. This allows some people to successfully make the transition needed to stop overeating.
2) Go cold turkey and have a reset. When you feel comfortably back on track, slowly reintroduce your favorite indulgences in moderate portions.

Keep trying; you only truly fail when you give up.

Just chiming in with good luck. When you refind your "why" it will all click back in to place. Take some time to find out what was easy and what wasn't and use that knowledge going forward.