You don't fail diets. Diets fail YOU.
Maybe consider taking an "explorer" perspective. You are traveling this unknown region and your job is to take notes and see what works or doesn't.
So which ones did you try? What about these diets worked/did not work for you?
If the scale is becoming your mood meter... what about going without a scale? What about using a tape measure? What about using nothing?
And what mental work are you doing to prepare for maintaining? Because that's basically putting in just as much work to STAY STILL. Not losing or gaining much. Just holding in place.
If your motivation is seeing scale move down, what will be your motivation to maintain?
Last but not least -- break it up in chunks. When the weight loss is big, it may be easier to lose it 10 lb at a time with some mental breaks in between.
If it makes you feel any better... I've lost and regain 80 lbs. I was within 20 lbs of goal... and slowly over years it came back on. So I know I can lose and I'm good at it. And I know I still don't know how to maintain. And here's what I've learned in my exploring...
1) Ok, it might take a few passes thru "losing" so I can take several stabs at maintaining to learn the skills. Fine.
2) Dude, next time at least keep up with the weigh ins even if the formal exercise and food log go to pot! Because then I can try to stop the slide at regaining 20, 40. Not all the way back to 80 back on!
3) It might take time. But the only way I FAIL fail is to quit. Trying is to have hope. It's fine to have to take a mental health break, but I will not FAIL fail. I will keep trying.
So... here I go again.
GL!
A.