I'm in the exact same boat. I've been yo-yo dieting and trying every diet under the sun for as long as I can remember. Not a day goes by that I don't look at myself and think yuk, get yourself together, but yet nothing changes! And here I am again, at the end of another year with yet more weight to lose from my Christmas binges!!
But, the biggest difference for me this year, is I'm completely letting go, in a good way! I cannot live my life constantly trying to lose weight, it's exhausting. And I plan, and plan and have the best intentions and then like you say, I'm failing before I'm even through the first day! So I've decided this year I'm really going to change my life style for the better, and change my mindset. No more calorie counting, no more scales, no more "I can't have this or that" I'm just going to take each day as it comes, make better choices and just focus on how I feel/how my clothes fit.
I'm sick of constantly going "I'm going to do X,Y and Z by this time next month" and then if I don't do one thing I hate myself. I'm just absolutely exhausted mentally. So I'm going to try my hardest to take each day as it comes and move my body because I want to, not because I have to, and eat better because it makes me feel better, not because I can or can't have certain things!
Sorry that got very long winded, I'm half thinking outloud! But yea I'm basically trying to make this year the biggest year of change, especially mentally.
Good luck! Happy to support along the way 💪🏼