I had the same reaction as @Kate, that this is an ego thing. Like, maybe now that you know your ex’s boyfriend is good with your kids — and that they like him — you now feel like you’re in competition with him. So no, I don’t think he was overstepping. I don’t have kids, so I can’t really relate to what this must feel like, but if you have complicated feelings over a new parent figure in your kids’ lives, I don’t blame you. I don’t think you should raise this as an issue with your ex, though, because this is a personal issue, not a co-parenting issue. If you need to sort out your feelings around this, that’s what therapy is for.