If the facts are as you present, it may be that the prosecutor will not go forward and dismiss the case. However, since charges have been made by the police, it is not the simple matter you think it is. If you are very low income or indigent, the court will appoint a very competent attorney to handle this for you.
This definitely sounds like intimidation and entrapment. As the others stated definitely talk to a supervisor at the State Police headquarters.
The public defender is your attorney. If you feel he is not on your side, ask the judge for a change of attorney. Speak to this attorney about your feelings in this matter.
As far as the civil theory of "social host liability" you would need to contact a civil litigator. He was responsible for his own activity as far as the charge of DUI and the social host liability law does not usually extend into the criminal charge arena. The fact that he was not a minor also negates this theory somewhat. He should talk to an attorney and try to plead this out.
If the police were not involved and you were not arrested, this event will cause no problem with your visa. They will probably send you a letter demanding some funds, but they do not usually take it any further than that.
You will definitely need the receipt from the casino if you filled out a tax form when you won. If you didn't win in a lump sum you will need to prove that you were there and were winning. You should definitely talk to a criminal defense attorney before you make any statements to anyone else.
You don't mention if you are a Canadian citizen. However, a warrant may well show up when you travel and cross the border. You should try to clear it up before you leave, speak with a criminal attorney.