I do not practice in your jurisdiction. However, generally speaking, if this is a charge that is criminal in nature then it is out of your hands now and is the state's hands and you cannot drop the charges. The case now rests with the state v. your boyfriend. I hope for your sake that things continue to go well.
Assuming the Commonwealth of Massachusetts is now prosecuting the case, the decision to proceed or not is now almost entirely in their hands. If the Commonwealth feels that a crime has been committed, it will almost certainly decide to proceed with prosecution. However, if you are the only witness and the only victim, you might reach out to the prosecutor and speak with her/him to get additional advice and let them know your position.
As others have told you, it is now out of your control to a great degree. Your boyfriend will fare best if he has an attorney. Without one, the DA will probably try to get him to plead to probation and a Batterer's Program. With an attorney he should be able to get the charges dismisses, unless he has some history of violence, and especially if he has any history of domestic violence.
There are means of dealing and trying to solve this problem. Your options depend in large part on what you said to the police. But there may be ways out of this.
Does this answer your question?