@HermesPasser
can't this stupid soldier understand the context?
Ethan's the one who didn't realize Cesar was talking about himself during the whole "I know this guy whose wife started talking about divorce when he got back from the campaign - do you think she might have been cheating on him?" conversation and helpfully volunteered that yeah, that's probably what she did and it's so common soldiers have a phrase for it ("putting her shoes on backward") before he realized Cesar was talking about his own situation, and he only picked up on that fact when Cesar broke a pen and ordered Ethan out of his office in a rage.
So Ethan's already primed to be on the lookout for signs Canaria is having an affair, he's predisposed to think that's likely, and he thinks Cesar suspects it as well.
Given that context, Canaria's reminiscing about younger days sounds
awful to Ethan. It's not like he can talk things out with anybody to determine the truth: if Canaria was actually having an affair with the second prince, of course she'd lie about it. Ethan can't confront the second prince on a mere suspicion, and if the second prince really was having an affair with Canaria, he'd lie about it too. All telling Cesar will do is fuel Cesar's paranoia, or lead to a confrontation with Canaria and/or the second prince, instead of helping either of these guys reach the truth.
Basically, Canaria said something incredibly dumb in front of someone who was going to take it in the worst way possible. Then he took it in the worst way possible.
@CivilSky
...it's just odd that he didn't find it strange that an order was sent in his name that seperated the princess and her bodyguard?
From what we've seen of Cesar, he probably found it odd, but since Ethan got press-ganged into guarding Canaria, she still has an escort, so Cesar's not too worried at that moment. He (or his smart aide) are probably going to have that maid watched from now on, though, unless they're idiots.