I hope it wasn't as painful to experience as it was to watch. Nothing much worse than absolutely demolishing your opponent only to fall prey to a simple back rank mate. Anyhow, not to rub salt in the wound (myself coming off a 2 game losing streak, one of them to a simple N fork) but I've posted elsewhere a blunder checklist and I can't recommend strong enough that you formulate and implement something similar. And what's absolutely crucial is that you follow it on each and every move as its the one time you skip that something like this happens. In fact, if you don't think you need to bother or feel the urge to skip, just think back to this game and how a single, easily preventable oversight cost you an overwhelming win.