You're probably feeling terrible right now. And that sucks. But remember, shit happens. And while ultimately you are responsible for your own success, it's your CEO's job to build the organization and make sure that people––including you––are setup to succeed. And my guess is that the organization itself is losing a lot by losing you. Bummer.
But as you will quickly discover, the past is the past in startup world and the only thing that matters now is what you're doing next. Enjoy the endless possibilities that are future. Be proud of what you've built. And be proud of yourself.