We cannot take this further than friendship
Though I was shocked to hear that you are falling in love with me, I must confess that I am feeling the same way towards you. There is such a strong attraction between us; that I cannot deny. Whenever I think of you, my heart skips a beat. The whole thought of us being together is so exciting and tempting.
Yet, when reality sets in, I realize that the stakes are too high to consider such a proposition. It would utterly destroy my __(family/husband and children/etc.)__ and I cannot bear hurting them in this way. Such a betrayal would be overwhelming and I don’t think I could ever look in the mirror again and feel good about myself if I went ahead with it.
As a married __(woman/man)__, I carry a big responsibility to my family. If I were to toss that all aside so that you and I could be together, I believe I will have not only failed myself but also those I care so deeply about. After giving great consideration to all of this, I’ve decided that I will just have to learn to keep my desires in check and squelch those feelings I have for you. Hopefully, you will be able to do the same so that we can remain friends.
I’m sorry if you were hoping for more from me, __(Name)__, but this is where I have to draw the line. My place is with my __(family/husband and children/etc.)__ right now and I believe this really is the only right thing to do.