Ladies: why do men lie?

My friend michael who i adore but who also makes me mental...lies to me. He will be brutally honest when it's needed. If you read my previous questions...then you know i'm over the moon about him. He told me the other day that he lies to spare my feelings...which is wrong but also a turn on. I'm gonna marry him someday when i'm thin and pretty. So ladies tell me why do men lie? If your husband sleeps with a hooker and 9 months later you are asked to go on maury...would you stay with him? Thanks in advance