Maybe my experience can give you another point of view or some ideas on figuring out what's next.
Happy to be a sounding board if you're looking more for that.
My email is in my profile.
OP's got a _lot_ going on here: fear of being stuck at a prestigious company; team/interpersonal struggles; the feeling of vulnerability from bombing an interview (which was also "the one" opportunity); possibly burnout; and the potentially very serious signs of depression. Thought I'd try to take a chance at demystifying some of the demons I know better, I'd probably learn a bit too.
Whether or not he or she reaches out, there are a lot of other great responses here, and I hope OP can at least feel less alone.
That said, I got past it, just as OP will.
I'm willing to do the same. Email in profile.
OP - I'm also happy to do a mock interview for free. Feel free to reach out (info in the profile), whenever you feel ready. [Disclaimer: I run a for-profit in the space, but we're all humans first]
Let me make you a deal: call me up and I'll interview you, no "puzzles". Except instead of this being about a job with me, I'll give you feedback from the interview and any advice I can. You can reach me at mikey@ (domain in my profile).
(Depression signs are another matter; others have given some good advice there.)