Once you have filed charges, the case does not belong to you any more. It belongs to the state of Maryland, which is going forward with the matter on behalf of you and all the people of the state. So you need to contact the prosecutor who is handling the case against your boyfriend and let him or her know that you have changed your mind and don't want to go forward.
You are the alleged victim in this case, and without your cooperation and if there are no other witnesses, the state won't be able to meet its burden of proof beyond a reasonable doubt. The prosecutor will happy to talk to you, because they will always talk to their complainants.
You should try talking to the prosecutor in person, rather than over the phone so that the prosecutor can see how serious you are about not wanting to go forward with the case. Tell the prosecutor why you do not wish to proceed and why you think you'll be safe from harm if the case is dropped.
In my experience, the prosecutor will probably tell you that it's too late for them to drop the case and that once a domestic violence matter is filed with the court, it becomes the state's case and not yours any more. He will also probably tell you that the state can choose to go forward with this case whether you cooperate or not. He may tell you that if you refuse to cooperate and testify against your boyfriend, he can subpoena you , bring you into court in handcuffs, if necessary, put you on the stand and require you to testify. He can tell you that if you change your story, he can charge you with perjury. These facts are all perfectly true.
However, as I mentioned earlier in this answer, you are the state's key witness. The prosecutor needs you. So he's not going to do anything to harm you. And if you stick to your guns and tell the prosecutor that you want the charges dropped, most prosecutors will eventually opt to cut their losses, once they are sure that nobody is forcing you to drop the charges, and once they are sure that you are going to be safe. Most DAs do not like to spend time, energy and money going to trial with a reluctant complainant and a case they are going to lose.
So if he won't agree to drop the charges, at that point you need to get a hold of your boyfriend 's lawyer and let him know you've been trying to get the prosecutor to drop the charges but that he will not do it and him how you can help him to get the case dismissed.
In my experience, when the complainant and the defense lawyer join forces to double-team a prosecutor to convince him drop charges, something favorable to the defendant, even if it's not a direct dismissal, can almost always be worked out. In part, this is often because the judge will get impatient and eventually get into the act and tell the prosecutor that he ought to resolve this and stop wasting the court's time with a case that is clearly going nowhere.
So, in short, the prosecutor is the only one who can drop this case, but the process starts with you letting him or her know that they don't want to go forward.