Harrment in the workplace? Help!?

Okay since the last month or so rumors have been flying around at my job that me and another employee are sleeping together. I am married and these rumors are taking a stab at my character. Anyways my GM jokes about our so called "relationship" and when other employees hear these jokes the rumors escalate. So one of my friends talked to a diff manager about what we can do to stop the harrment and hse said she has proof we are actually sleeping together and that I was spreading the rumors myself so it was my prob. I didnt hear her say this my friend did. So I talked to a diff manager about it and she wants me to doent everything. I have to give ehr the letter tomorrow and I dont know how to start it what to say or even who I am writing to I need tips and I need help! I wish I would have left things alone and not got thi 3rd manager involved because she is pretty persistant about putting a stop to all of this but its making me uncomfortable I dont even know what to write HELP ME!