Dear…
It is true that whenever you are near me, my heart skips a beat. And when you kissed me the other __(day/night)__, oh how the burning passion within me was ignited. There is a strong attraction between us; that I cannot deny. To have an affair with you would be wild and exciting and is so tempting.
Yet, sadly, the reality that surrounds such a proposition is too risky…the stakes are far too high and I know I wouldn’t be able to handle the stress that would come with weaving together the endless lies to hide our clandestine meetings. How worrisome the risk of getting caught would be, I would forever be watching over my back. And the daily guilt...I wonder if I would ever be able to look in the mirror and feel good about myself again. Moreover, I cannot not bear the thought of hurting the other people in __(my life/our lives)__. This would destroy them and they mean too much to me to put them through that.
As __(married people/ a married woman/man)__, __(we/I)__ carry a certain responsibility to the other people in __(my life/our lives)__. If __(we/I)__ were to move ahead with this affair, I believe that __(we/I)__ will have not only failed __(ourselves/myself)__ but those __(we/I)__ care about too. So, with all this in mind, I’ve decided that I will just learn to keep my desires in check and squelch the feelings I have for you. Hopefully, you will be able to do the same so that we can remain friends.
I’m sorry if this is not the outcome you were expecting, __(Name)__, but in the best interest of everyone concerned, I believe this really is the only right thing to do.
Sincerely,