Your partner will not cease behaving like a child unless you cease behaving like his mother. But you will not, will you? Because when he “grows up” he will get the right to vote and you will have to take it into account and won’t be able to wave it aside. It is much easier now: don’t anger your Mummy, Mummy is tired, live me alone, you can only think of games, get a life, you are a disaster for me.