Dear Mother of the Other Woman:
Are you happy now that you supported your daughter's relationship with my husband? By supporting their affair, you were also supporting the destruction of my marriage, the destruction of my kids' relationship with their father, and the destruction of your daughter's self-worth.
What kind of mother encourages her daughter to sleep with a married man?
My husband and I are working through this crisis. My marriage and family will survive and even thrive. But from what I've heard about your daughter's behavior since their breakup, she's not as resilient. Maybe the next time she tells you about a married boyfriend, you'll have enough compassion for her and everyone else involved to tell her to back off.