If you want to keep the family together, you need to calm down and decide how to behave with her husband's mistress, to eventually win over it a victory? The main rule: don't go on about the emotions! Emotions can push you to actions that you will cause harm. Therefore, no matter how difficult, try to pull yourself together.
Do not stoop to having to physically deal with her husband's mistress. First, it's just not civilised. Second, it can be stronger and then you will suffer, and its actions will be regarded as legitimate self-defence. Thirdly, you can be prosecuted. Finally, you will look in the eyes of her husband's angry, jealous drama Queen.
We should not profane mistress, spreading slander about her. And especially don't try to soften it, claiming that it breaks the family. Even if the mistress will experience embarrassment, awkwardness, hardly she decides to terminate the relationship with your husband. After all, a woman dreams of personal happiness. Besides, she can fend off your accusations, complaints compelling argument: "it's her fault, it would be my husband spending time with you, you would not change a thing!!"
Defeat the mistress of her own weapon. Try to find an answer to the main question: why all this happened cheating husband, what is a mistress better than you? Honestly and impartially assess your appearance, analyze their behaviour (including in the intimate sphere of life). Even if a mistress younger and more beautiful you – don't despair, you can still improve.
If your figure is "broke", do some exercise, adjust the diet, removing from the diet fatty foods and sweets. Pick up the original hairstyle, makeup, update your wardrobe. Resolutely refuse shapeless robes and a broken home sneakers, even if they are very comfortable. Husband needs to see in you the interesting, beautiful woman.
If you have treated intimacy as marital debt, no wonder your husband has a mistress. Try to behave in bed more relaxed, freely. Find and read literature on the subject of sex, if possible go for consultation to the sexologist.
If you were too demanding, bossy, picky, "suppressed" husband, make radical adjustments in their behavior. Take care of yourself, try to become more relaxed, flexible, and friendly. And then sooner or later the husband will make a choice between you and the mistress are in your favor.