Usopp didn't have to apologize and go back to the Strawhat crew. He'd do all right, here in Water 7. They wouldn't really need him. He knew that now. Perhaps rescuing Robin would have been more difficult without his assistance, but at the end of the day he was nothing special and he was certain he wouldn't be missed - he watched the crew go about their business and party as seemingly happy as ever, and their backs were turned to him as he stood on the docks. He opened his mouth to call out their names -
And saw Franky, shipwright and sniper all in one, who counted as a crewmate because he had fought alongside them, but didn't they remember the way he had demolished their skinny, weak sniper, didn't they want to wait for him? But what use did that collection of odd, wonderful, amazing people have with a guy like him?
The words died in his throat and he watched them go. In their shiny new ship, they'd soon forget about him. He apprenticed himself to a carpenter at the behest of the weeping Franky Family, who welcomed the help. It was an okay life, but with every day that went past, something bitter and twisted he kept buried deep in his gut like a small creature in its cage got loose and grew and grew and grew. Before he thought about these things every once in a while and they spiraled ever downwards until Luffy or Chopper dispelled them with a glance. Now, it was harder to keep the thoughts truly at bay. A scant six months later, he impressed a large pirate crew with his sniping skills, and they gladly took him on board.
That was the dream, right? Not to be a man who traveled the seas with the pirate king - because Luffy would be the pirate king, whether he was with him or not, that was a fact - but to be a man of the sea. He wasn't unhappy, but some days he would stare out at the sea as he did as he waited for his father, and wished to see his captain's wild grin and the faces of his crewmates once more.
Maybe if he tried hard enough and proved himself, maybe they would take him back.