First off, thanks for reading! To be honest, I really didn't expect to get this much attention. This is a story that I've wanted to share with friends and family for a long time, and was thoroughly surprised when it was picked up by Backchannel (and then posted here).
Regarding some of the points made here, I (mostly) agree. Getting into YC or raising money is not success. Changing your idea completely isn't really a "pivot" (but I don't know if the industry has as concise of a term for throwing everything out and starting over). In my mind, the real failure was squandering the opportunity of YC, an opportunity I know many people would kill to have. Clearly we should have stuck it out with our idea, but we were 21 years old, stressed out, and foolish.
I also want to note (in case anyone was wondering) that my experience hasn't diminished my opinion of YC at all. PG's advice was spot on, and YC remains an amazing program for founders. We simply didn't make the best use of our time in it.
Hopefully reading about my experience is helpful in some way. If not, sorry about that. Give it a downvote and send it on its merry way.