FS: I've already changed the locks not that long after BD because the lock broke. H was a bit anxious about this and then I gave him a key. It will look deliberately inflammatory to change them again. And H has always been like that about making changes to the house, the few things I've chosen by myself have been criticised mercilessly. That's why I told him when I bought my new car he wasn't allowed to complain about it (and he hasn't). I don't think H has separation anxiety about the house because he's always been critical about me doing things in the house (is it still territorial though? It feels like a power thing though I've always been careful to involve him in most decisions, like I'll give him 3 paint colours to choose from and then give him the final say). He might have finally realised though that I've moved almost all of his stuff out of the wardrobes in the bedroom, so that might be one reason why this happened!
I'm not going to start a full scale fight over this, but I am going to make it clear that it won't be happening again. And I'm asking for my car key back, there's no reason for him to have it in his flat because if he's using my car then it'll be because he's here to take one of the kids somewhere when he doesn't have his car.
I am super tempted to give him a bag of my dirty laundry tomorrow night though and say that I'm sure he won't mind doing mine if he expects me to do his