I've got 2 children with my ex, and I've been with a new partner for almost 2 years.
We get on brilliantly when it's just me and him, but despite saying that having a family is all he has ever wanted, that's not how it seems when he spends time with me and the children.
He always seems to be in a grump about something. Whether it's their table manners, or how they treat his dog, or that the kids are grumpy about going out somewhere, pretty much every time we are together with the children around, he seems unhappy.
I can't imagine how difficult it is being a step parent, especially as we've had chats in the past about it being me to do the discipline rather than him, which I know he finds difficult. But it happens every time he sees them.
I haven't brought it up with him, as I don't want to make him feel bad when he obviously struggles with it. But I also find it difficult to deal with. Maybe he likes the idea of a family more than the reality?!