You must realize that you are 54 years old, and I have certain needs which you are no longer able to satisfy. I am otherwise happy with you as a wife, and I sincerely hope you will not be hurt or offended to earn that by the time you receive this letter, I will be at the Grand Hotel with my 18-year old secretary. I'll be home before midnight and will see you then.

You, too, are 54 years old and by the time you receive this letter, I will also be at the Grand Hotel --- with our 18-year old pool boy.
Since you are an accountant, you will appreciate that 18 goes into 54 many more times than 54 goes into 18. Therefore, don't wait up.