Move on with your life

You may be a good student in China. However, you are too naive in USA. You should let the court drop the case and move on with your life. Once you have a criminal record you will be extremely hard to find a good job. Spouse abuse is not easy in your situation. You are not married and you do not have direct evidence for abuse such as a physical wound/injury or a doctor's letter. Many lawyers want retainer fee up front. Very unlikely they will agree with contifency fee.