You now know that she’s emotionally done and has established a “friendship “ with someone new, whom she now has a sexual relationship with. You need to begin documenting everything. You need to remove yourself off of all social media (evidence from social media can and will be used in court, yes, even family court). You need to hire an attorney, and file for temporary custody of your daughter. As others have suggested, hire a PI that will help prove her “affair” and gather your own evidence (texts, receipts of lingerie,phone records,etc) everything that you can to build your case. And enroll both your daughter and yourself in therapy, you’ll both need it. Don’t speak to her except in written form (text, email) they can be used as receipts too. Once again document EVERYTHING! Most importantly, don’t bash her in front of your daughter. Keep a diary to vent to, but DO NOT speak negatively about her in front of your child. Good luck!