Thanks! Can't edit my post, but didn't expect such a positive response, really cool to see others offering an ear as well.

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.