He's right

I agree, he's right. But at the same time, the moment he shouted, he was no longer simply right.
Also, it might have been a discussion about a very important matter, but at the same time it was a private one. Can't she express her thoughts to her future husband without the shounting? At least that would have been my thought pattern.

So, yes him shouting was wrong, but this is something he's brought up several times and she always ignores him on it. She should also respect her future husbands thoughts, and more importantly his position in the situation as well. He's a knight charged with protecting the kingdom and prince. This marriage would help there. She's being insensitive as well. But, again I do love them both and this is a situation they need to talk out. I just hope it doesn't go the "I was completely wrong, you're right Merielle(?) let's snoop and stop this" route because that would be so fake.

Yep, in a way, I hope both realize that the discussion could have gone better on both sides. That would be the healthy way of going forward as a couple.
One thing I am curious about is why does the thief seems to know why the MC shouted (talking about insecurity), I think I am missing something. I will enjoy re-reading to make sure.