In chapter 210, his eye is sort of... well, the best way I can describe it is that he looks like he's in a daze. Maybe something unexpected happened, which led to him having to leave the friends he's made, and everything is happening fast. When Nirei tries to get him to stay, that look in his eye doesn't go away. In fact, the only thing that changes is the fact that he no longer tries to force a smile. Until he says, "We aren't anything." In the manga panel, he looks thoughtful, like he tried and failed to find any significance in their relationship, but your honor, I want to introduce the idea that maybe he was disconnecting himself from the scenario in order to make it easier.
Suo has no problem pretending, as he's been very secretive throughout the entire manga. When Nirei attempts a punch at him, he gets this little shine in his eye, like "wow okay he really wants me to stay," or, more accurately, realization. He then proceeds to tell Nirei that his need to question things has always pissed him off. Uhm, what? Your honor, this is bullshit. Well, maybe not entirely, but I digress. If anything, it probably worries Suo, as his carefully maintained secrecy and image could be found out if Nirei had even the SLIGHTEST clue in the right direction. More importantly, however, I think this was Suo's way of reinforcing his decision to leave for the greater good through this disconnect and facade. He had to make Nirei hate him, even if what he had to say wasn't true. Which all trails back to the fact that he refuses to connect or be vulnerable.
Which I will now try to connect to the latest chapter, 217. If you've stayed through this entire tangent, I am genuinely surprised...
Anyway (x50) Suo is portrayed as a mediator, and his new trio of absolute BADDIES are constantly at his side, so that means they likely come as one unit in RC. Since Suo's an officer, they're probably his seconds or something. We see that they seem to be at least SOMEWHAT responsible for the training of younger members, as well as the care of abandoned or impoverished children. The chef mentions that there are less children that are being abandoned. This implies that taking in these children is not new. My first thought upon reading that was: "Suo had to have been in that position once." His old master might have saved him, and RC welcomed him in, so he feels indebted to the town to an extent. That doesn't mean he doesn't have genuine care for them, as a the end he also says "there are some things they're better off not knowing," which I see as his way of protecting them, but it could give more insight to his reason for leaving Furin. It also tells a lot about the way he shows his care in general. He did the same to Nirei and the rest of Furin, leaving them in the dark about a lot of things for the sake of what seems to be the greater good.
Overall, I think Suo is super cool. This was a lot of nonsense rambling, so I really hope it made at least a little bit of sense. Tumblr is my soapbox, much to the dismay of the general public. I am sleep deprived and felt the need to talk about Suo.