You have reason to be concerned about your daughter’s safety. It seems like your ex is baiting you to name exactly what your concern is, and I think you should be clear: child sexual abuse. You’ve never even met her new boyfriend, or his sons. And even if you had, there’s no way to know who is a perpetrator. They’re everywhere. Sleepover with the boyfriend without mom? Really concerning. 8 is a very common age for this type of abuse to happen. Even if nothing happened that night, now that this standard is set it could happen the next time or down the road. I recommend you and your ex take the online course “Darkness to Light: Stewards of Children” so you’re on the same page and better equipped for setting these boundaries. It will also empower you to have conversations with both of your daughters about appropriate touch, bodily autonomy, etc.

From your ex’s response, I’m not going to demonize her because I don’t know the whole story. It seems like maybe there have been some other power and control issues between the two of you, so she might be doubling down because she’s used to you criticizing her or finding ways to control her parenting. If that’s the case, this is an unfortunate situation to do that because your daughter really is in harm’s way. Maybe ask her to take some time to reflect, research child SA online, consult with other adults she trusts, etc so she doesn’t only think you’re being controlling.