Your experiences mirror so many of my own. I'm a physics guy and I poured my heart into school as well. I'm in grad school now and I'm about to drop out because I can barely even convince myself to get out of bed in the morning. I'm in an extremely dark place too. I am basically just massively self destructing for no 'reason' at all. I wish I could tell you what to do but I don't know myself. It seems success has only made me lonelier and more self hating. I used to really really believe that I could have a meaningful life by helping others, in whatever way I could. I lost that somewhere and I think the thing I need to do is find a way to believe in that again. To make it meaningful. There's a Nietzsche quote that's always really stuck with me "With a why to live for man can endure any how" I think even at my worst in terms of depression I've had a why for most of my life, a reason to live, despite the hard things I've had to go through... Just don't frame your life as a failure because
by some metric you will always be one. For my whole life I've been a failure no matter what I've done, in my own mind. I would just say keep going on. None of this makes you any less valuable than any other person on the planet. I hope my rambling is of some help