回复：回复：Don't lie

You have to decide whether you want to spend the money to hire a private lawyer.  I can only tell you the law and other facts. 

Both public defender and prosecutor are extremely busy, it is not uncommon that they talk only that morning before the trial.  Even if you have private lawyer, he/she might not be able to talk to prosecutor until trial day.   Despite of lack of witness, Prosecutor might still push you to plea guilty.  In this case, since they don't have a witness, you should push for trial because aquittal is likely.  

See following websites for more information.
http://www.masslegalhelp.org/domestic-violence http://www.masslegalhelp.org/immigration/grounds-of-deportation-for-criminal-convictions