I am so sorry. Your H is not acting in your kids' best interest, but he doesn't seem to get that. Sadly, he couldn't enjoy his time with them without needing to see the OW. That's just pathetic. You'll need to talk to a lawyer, but since your H left the kids with you and he doesn't have a visitation/custody order I would assume the role of the custodial parent. Until ordered otherwise, you make all of the decisions regarding the best interests of the kids. If you don't trust your H to make good decisions than tell him he'll have to visit the kids at your house. Again, talk to an attorney. I wouldn't want you to do anything that could jeopardize your case. Document everything. It's sad that it has to come to this, but someone needs to protect your kids' hearts and minds.