Dear Susan,

I am writing to tell you that our relationship must end, I am not the man you think I am. For a long time I have been sexually attracted to your sister.On several occasions I have had sex with her and I know you will find this unbearable.
What is probably worse than sleeping with your sister is the fact that I have also been having a sexual relationship with your mother.
Add this to the fact that, after a drunken night out, I had anal sex with your brother, you will now see what a terrible person I am. One final confession susan. Shortly after I started a sexual relationship with you, your father started pestering me for sex and yes I gave in to him.
And so Susan you must now see why I must end our relationship. I know this is all a shock but it is better out in the open. I am so very sorry if I've hurt you,I never meant to.

Your loving brother, David xxx