You fail because you lack focus and your self image is poor. You berate yourself for your current appearance. Lift your head up. Believe you can change.
1st, you have to make clear the vision you have for your body. It sounds like you've said what you want to be at weight wise. Now right that down on a white board or paper and put it somewhere that you will see it every day. This will help keep you focused.
Create 3 or however many power statements, "I am beautiful" "Taking care of my body is important to me" "I am changing the way I eat" stuff like that. Write those statements out on post it notes and put them in places you frequent, your bathroom, car, closet door etc. Read them each time you see them.
Your sweet tooth is all about habit. Cue, routine, reward
Change the routine. Your reward is you feel satisfied from tasting something sweet, so basically you want satisfaction. You can get that from other things than sugar. Like instead of the routine of getting the sweet treats get up and go for a brisk 5 or 10 minute walk. Trust me you will feel invigorated and energized and no longer desire the sweets. Then you must identify the cues, the things that trigger your desire to get satisfaction through your regular old routines. You might see someone else eating a sweet or see a commercial, or maybe there is an emotional cue that sets you off on the cycle of cue routine reward.
Learn thoughts cues, right them down and purpose in your heart to do your new routine of walking or whatever to get you to the place of satisfaction you desire.