Why? to convince her to leave for your sake? That'll never work.. To tell her what a slut she is? He's lying to you, what makes you think she even knows he's married? To really get rid of her? Don't send a letter, instead send her (1) a copy of your marriage license (2) a family picture and (3) a copy of the divorce settlement stating how much he will receive after you squeeze him like a wet sponge.. If she still feels she can survive on his new-found poverty, then they deserve each other.
If you insist on sending her a letter all you need to say is, hello.........should you decide that you want to stay with my husband I thought I would introduce myself as the woman whose house, car, nails, hair, and alimony he will be paying for many, many years to come.
First of all I wouldnt say anything. Obviously he is no good. What will you gain out of saying anything to his mistress! All that would do is make him think he is the MAN for having you fight for him. He don't deserve you.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them