The anger at least is expected - Hades has always been the grumpy one, and so Hythlodaeus does not flinch away at that.

"What are you doing, Hades? You came back late last night, too, and would not tell me aught... Is something going on?"

Despite everything, his voice is not accusing, plaintively inquisitive instead. It does not occur to him that Hades could be keeping any real secrets from him; rather, he's simply worried because withdrawing is usually his friend's way of reacting to stress, a fact that their neighbours have certainly learned by now, given how often Hythlodaeus would have to calm Hades down and bring him back home.