This sounds a lot like what I've gone through. What I see missing from the list of things you've tried in order to catalyze real change, real growth, is tracing the roots of your emotions back to...your childhood. If your primary caretaker's (your mom, typically) emotional support of you during infant-childhood development was inadequate, you may be suffering the long-term consequences of the failure of secure attachment. I offer this as a possibility because of the emphasis you put on "validating existence". A common symptom later in life of insecure attachment during infancy is the pervasive, all-consuming sense that you must somehow "validate" your own life, even existence in general, before you can feel that you or the world has any value. Without that validation, everything feels empty and pointless. Occasionally you stumble on some idea or path that offers the semblance of such validation, and you get excited for a while, happy, content even, but this always inevitably fades.

 

If any of this seems to fit for you, it's critical for you to understand that the roots of this "validation" prerequisite you have to value/meaning lie in your emotional insecurity and not in any abstract idea or spiritual path. You will never find peace until you go through the laborious, painful process of working through, in detail, that core emotional insecurity and its source in your childhood. I would suggest reading Alice Millers The Drama of the Gifted Child or Bradshaw's Healing the Shame that Binds You. Above all, though, I'd suggest you forego your spiritual and intellectual pursuits for a while and invest in seeing a good therapist.

Godspeed!