Legal Question in Criminal Law in Missouri

Yes. First tell the prosecutor that you will not testify against your boyfriend, and that you want to sign an affidavit of non-prosecution. If the prosecutor insists on serving you with a subpoena and putting you on the witness stand, you have to give your name, but immediately after that, answer every single question with:

"I decline to answer based upon my 5th Amendment right not to incriminate myself." Don't let the prosecutor trick you into answering any questions. If you do, you will give up your 5th Amendment right and can be compelled to answer all the rest of the prosecutor's questions. Write down the "magic language" quoted above, take it to the witness stand, and read it exactly the same until the prosecutor gives up. Be strong!