If you are in a startup, you've already won. You've already done what millions of people dream of doing but never had the balls to do. So be proud of what you've achieved! You are awesome.
As a dev, I feel really really sympathetic towards your situation. However, it's the reality of the business. I've written things that leverage certain APIs and ended up getting replaced by "the official version." Yes, our apps bring traffic to their site, but it's also a two way street. By leveraging APIs, we are taking advantage of their users and infrastructures. So yeah, it sucks that it ended, but at least it was fun (hopefully profitable) while it lasted. Move on bro!