I've experienced something similar, I think: the older I get, the more I despise myself for not becoming the person I could have become had I put in the effort when I had the chance. I had talent and potential once, but I feel it's too late to do much with it now, and the opportunities I may have had then have now passed me by. Failures of the past condone failure in the present, thwarting any success that could have come in the future. Self-doubt is indeed a devil of the mind, turning us against ourselves before we even begin.
What have you to dislike, though? I think you're terrific—bright, devoted, inspirational, and so much more—and I'm stunned that you don't see it. Maybe I presume too much, or maybe I've read too much into your posts (and at times the disappearance of them—tsk, tsk), but I believe that you could really make a difference in this world, that you have that kind of fire in you. You just have to learn how to let yourself shine.