Ah, what a good question again! That really got me thinking, and I realised I don't think that's going to be dissected explicitly in this story, so I'll try my best to explain what I think I tried to do as well and as briefly as possible
So, in the Percy Jackson story, Nico is someone who tends to be looked at by others as dangerous and scary. Creepy, even sometimes. He's also suffered a lot of loss of people who did love and accept him in his early life. So what I think I was trying to do, was write him as someone who's coping styles were built up around "rejection" based trauma. (Some other examples of backgrounds that can have a similar effect are being bullied, or having emotionally abusive/neglectful caregivers). Of course everyone reacts to emotional trauma differently, but I made Nico more avoidan/fatalistict in how he tries to remain in control of situations (Don't get attached so people can't hurt me, leave them before they leave me, expect the worst so you can't be disapointed, block out all negative feelings) to contrast Logan's confrontational coping style. Aside from that I made Nico more internalizing (Turning his feelings inward, shame/self blame) to contrast Logan being externalizing. That's probably their biggest difference, and biggest source of conflict, actually. In that sense they speak completely different languages.
Of course when it actually comes down to it, I'm just using the poor guy to deal with my own issues. Like all of this story, it's all just me projecting Even Aphrodite being upset, is just me being upset with that part of me haha.
Sorry for the giant essay! And thank you so much for sharing! It really helps me reflect.