I want charges dropped against my spouse who was arrested for domestic assault against me. I called the prosecutor to ask him to drop the charges against my spouse. He said he would call me back with a decision. He did not. So, 4 days later, I called again to ask him. Instead, one of his assistants told me that I should not have contacted him, because that "could make him a witness himself," whatever that means. His assistant told me that when the prosecutor has a chance to read the case, his office will contact me, and that I could come in, and with a third party present, talk to the prosecutor. I would rather just email the prosecutor than come in to talk to him. If I email him, listing the reasons that I want him to drop the case against my spouse, is that legal?
The prosecutor has valid concerns. What you're providing her is considered exculpatory or mitigating evidence under Brady v. Maryland, so she has a duty to disclose everything you told her to your spouse's attorney. There are a few circumstances where the prosecutor can be made a witness, like if you made an inconsistent statement to them, or told them you didn't want to prosecute, then didn't testify at trial. If there's a third party there, that third party can provide that evidence at trial.
Keep in mind, the prosecutor doesn't have to drop or dismiss the case just because you don't want to proceed. In about half of all DV cases the victim doesn't want prosecution or is too scared to testify. Spousal abuse is rarely a one-time event and victims of domestic abuse are much, much more likely to become murder victims. It's critical to document past abuse and begin rehabilitative intervention counseling.
There's probably nothing illegal with you emailing the prosecutor, you're a victim in a case.