She's dating someone new and wants him around the kids already

Found out through my daughter that mom's new boyfriend came to a family dinner last weekend. We've only been separated for 6 months and this guy apparently stayed over. I don't want to be that guy but I'm not comfortable with some random dude having that much access to my kids this early. We don't have anything in the custody agreement about this. Should I bring it up or am I overreacting? Part of me knows she can do what she wants at her house but it still bothers me.