If Nico was upset, you could count on Will to literally drop whatever he was doing/holding and run towards his Greek warrior in black as fast as he could. Some say he even tried to light travel once or twice, just to see if there was an even faster way to get to him.
Nico hated it, though it was always welcome.
He didn't like the fact that Will dropped an open flask of nectar when Connor Stole told Will he heard a scream coming from the Hades cabin, or the fact that when a camper told Will he was crying in the depths of his room Will ran from the infirmary with such speed he missed arrows by a half an inch or less aimed for his head.
But what Nico hated most of all was the fact that Will Solace died trying to get to him while he sobbed over Hazel's cold, dead body.