This reminds me a little about about what happened with Mark Zuckerberg and the Winklevoss twins. Communication was cut off for a while and many excuses were made. However, if it makes you feel better, the twins now have a $150 million stake in Facebook. [1]

Anyways, I'm not sure if I have much advice. First thing should definitely be hiring a lawyer, though. You should probably refrain from posting anymore information here on HN as well. I've seen you've already removed some, which is good. We only need to hear the gist of the situation (for future reference).

Hope everything turns out well!

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[Added in edit]

I traced back to when you were first starting this project. One of the people commented and wrote:

   I see these types of posts and it astonishes me that people will look for
   cofounders "on the street."

   I can't imagine that [ increases the odds of being successful -- but maybe I'm
   wrong. Employee number 5 can be an unknown quantity,
   but employee number 2? That would terrify me. [2]

This should be a warning to everybody else.

[1] - http://www.sfgate.com/cgi-bin/article.cgi?f=/g/a/2011/01/04/...

[2] - http://news.ycombinator.com/item?id=1625890