He lost her...
In what started as a normal day, with the Strawhat Pirates, with Luffy, Usopp and Chopper being idiots around the Thousand Sunny, Curly-Brow cooking up dinner in the kitchen, and Franky inventing who knows what for the ship, and lastly the only two females on the ship, were relaxing on lawn chairs, with Brooke playing a melody for them on his violin.
And Zoro as usual was working out, doing push ups not far from Nami and Robin, instead of up in the look out like he normally does. It was such a beautiful day, and he, like the rest of the crew, didn't want to waste it. Besides, he wanted to be next to her.
Nami.
Lately, things between him and Nami, were tense, and he couldn't figure out why. After being separated for two years and then see her again, he realized that the empty feeling he felt was gone. At first, he thought that the fact that he and the crew where separated for two years after a horrible fight, was what was causing the empty feeling in his chest, but he was wrong.
He missed her.