my biggest mistake is sleeping with you, even though i know you're perfectly happy and married to her.
we both now have a secret that can never be let loose.

the biggest part of this mistake is that i've now turned you into a living lie, always lying to her to keep her happy, thinking she has the most perfect husband in the world.
i'm sorry that i did this to you but not sorry it happened. you could have stopped it whenever you wanted but you didn't - i knew you wanted me too.. not only as your best friend but as a lover.