Harry's reasons for keeping the relationship between Thomas and himself secret has been repeatably gone over in the books. And the theme again gets raised in Battle Ground. He Who Walks Beside used the relationship to attack Harry through Justine. I'm assuming that Beside has the same or better ability as has Anduriel. I take this from Titania's warning to Harry in Cold Days. Telling Carlos represents an unacceptable level of risk. There is a movie interpretation of this type of ubiquitous surveillance, called The Conversation.
What was repeatedly stated in the books was that the WCs would use the divided loyalties against them, but I do see your (and Eb's) point that family relations should be kept hidden so you don't make them targets.
@Dina: I agree that after Harry learns about the engagement, Harry should say different things than before.
I do wish Harry had told Carlos off somehow. Harry has been repeatedly let down by the Council starting when he was
six freaking years old.
If the Merlin was kicking Harry out for any rational reason beyond not trusting him, I don't think it would be so Harry could act as a spy. A spy who isn't reporting back to you isn't any good to you at all.
The Merlin approaches Harry to get him to act as a spy. Either directly or through an intermediary. Here's a scenario that could explain the vote of at least one of Harry's/Eb's allies on the SC voting to kick Harry out. Let's just go with Rashid, who voted that there was no Black Council in TC. To bring an issue before the SC requires a vote of three. Let's say it's the Merlin, Ancient Mai, and Rashid voting. (We could, but don't need to add Martha and Cristos). The Merlin explains to Rashid (and/or Martha) what he's planning. They all agree that Eb and LtW wouldn't go along with it, but will once backed into the corner of a vote already made. After Eb and LtW get out of the hospital, any combination of Harry's allies on the SC plus the Merlin can approach Harry and ask him to spy.
Sure it makes a lot more sense if Harry agrees to it before hand.
Mai and other wizard explained the whole Council what Mouse is.
Not really. They only explained that he was a very reliable witness, and Mai expressed shock that Dresden was allowed to keep one.
But the real decision came at the end after he took the eye of Balor obviously because he did not trust the white council with it.
Didn't they kick him out before he even had a chance to turn it over to them?
I suspected Fidelacchius will be able to cure the nemfection since it was explained how it works (but it could be that it can't work against Nemesis ...
Amoracchius was effective against Outsiders while Eb was having trouble with them. (PG)