Greetings. Yes, you can send another man a letter like this. The better question is what are you going to do about your marriage?
Without sounding harsh, I think you answered your own question. You communicate, legally and forcefully, that if he does not break off contact that you would file suit against him. Before you send the letter, ensure that you are truly ready to file a lawsuit. A letter with an empty threat is worthless. Good luck.
Janet L. Fritts
Attorney with Rosen Divorce
4101 Lake Boone Trail, Suite 500
Raleigh, North Carolina 27607
The response posted above is based upon the limited factual information made available and is not intended as a full and complete response to the question. The only reliable manner to obtain complete and adequate legal advice is to consult with an attorney, fully explain your situation, and allow the attorney sufficient opportunity to research the applicable law and facts required to render an accurate opinion. The basic information provided above is intended as a public service but a full discussion with an attorney should be undertaken before taking any action.