Yeah, I'm pretty sure that's it. Nadan said a few times that he doesn't like what Suu is doing. I'm pretty sure he knows that Suu killed people and he doesn't want him to keep doing that (or any other shady business). I hope though that they'll be able to get along again later, because Suu cares so much abouth him.
It kinda annoys me a lot about Nadan. If Suu hadn't done the stuff he has done then Nadan would already be dead. Nadan is connected to a family charged with high treason. Literally Suu did all these shady stuff because it was the only way for both of them to survive and all Nadan can do is whine, "yyoooouuuu're so baaaaaad!"
I get it, Nadan. You want the nice guy persona, but for you to be a "nice guy", Suu had to be the bad guy. Nadan is a very black and white thinker. He does not do complex and grey morality. Poor Suu.
We see the past how Suu and Nadan were close as kids, and Suu worked and sacrificed a lot to buy Nadan’s freedom, however Nadan treats him so coldly now. Suu has mentioned several times how things aren’t the same between them anymore. Is there a clear reason why? Is it because Nadan disapproves of the illegal/manipulative things Suu does to protect them both?