First off, I'm very glad the OP was brave enough to tell his story. I'm sure he knew he was going to get whopped upside the head for it, and he did.
But my guess is that bad judgment like his isn't uncommon, but we rarely hear about it because people know better than to open themselves up to this kind of criticism.
I have had dives where I have made questionable decisions, and I've had the thought run through my mind, "If anything goes wrong here, SB is going to have a field day with it . . . "
The OP is, I suspect, relatively young (judging from the comment about talking to his mother) and probably male, and has just enough experience to think he can take on more than he really can; and he probably had a knowledge deficit regarding decompression and gas management, as well. None of that excuses his actions -- I know our OW students have to do a knowledge review that specifically asks if one can use one's buddy's computer, and a question which asks about what you do if your computer fails (and the answer isn't borrow one from somebody else!) But I think there is huge value in having other young, relatively novice divers read a story like this, and see how easy it was for the OP to make a whole series of bad decisions, without ever really stopping to consider whether there were bad consequences that would ensue. It's cautionary, and someone who has read this story might stop after the first bad decision, to ask himself whether the cascade really ought to be stopped there (or even before the first one).
It takes courage to do this. Thank you, themagni, for sharing your story.