My ex has told DS (five) that she's a friend. This was a few months ago. Since then, the relationship seems to have progressed a lot, with her joining my ex and DS on the weekends DS's with his dad, and - according to my ex - them being increasingly affectionate around DS. It looks as though she will now be moving in.
My ex has no intention of explaining to DS that the relationship has progressed to her being more like a girlfriend; he says he'll answer any questions if DS has them. But I feel that DS should have it explained to him, however casually, that Daddy has a new partner. I don't want him to feel confused by catching them smooching in the kitchen. I don't want him to think that "friends" go round squeezing each other's bums. So I've been fighting the urge to tell DS, mindful that it's my ex's business and he wants to deal with it his way. But DS is my business, too.
Shall I mention it to DS, kind of in passing without making a big deal of it? Or do I need to be respecting my ex's wish to keep quiet about it? If I had a new partner who was becoming pretty obviously serious, I wouldn't dream of not explaining it to DS!