The Strawhat crew was absolutely crazy. Brook adored it. He hadn't thought he'd ever find such great companions again. He was happy down to his bones - and he should know, because he was a skeleton! Yohohoho.
Brook fit right in, with hardly any tuning. He made music with Franky and told stories with Usopp. He laughed along with Luffy and Chopper at the most ridiculous things. He shared history with Robin and got smacked around by the beautiful Nami like everyone else. Zoro appreciated his swordsmanship and Sanji liked the challenge that came with feeding a skeleton. It was fantastic.
But that didn't mean there wasn't any drama. Brook hadn't thought anything about asking how long Sanji and Zoro had been together. The absolute chaos it caused broke the Sunny! Apparently, neither of them had realized that everyone knew, even young Chopper. Why they thought it was a secret was a mystery, when anyone with eyes could see that they were an item. Brook saw it and didn't even have any eyes, because he was a skeleton! Yohohoho.
Brook enjoyed that joke, even in his own mind.
Sanji and Zoro weren't pleased with Brook, or the others. They skulked around the ship like wet cats, hissing and spitting at anyone who came near. It was terribly funny. This crew was so amusing! Brook was glad he joined them.
"When did you know?" became the game amongst the Strawhats, much to Sanji and Zoro's chagrin. Stories were shared about Sanji's missing tie, Zoro's rare smiles, and fights that dissolved into suspicious silence. Brook felt like he'd come late into the game; Sanji and Zoro had been in love for quite a while. Brook had missed out on watching the romance blossom and grow into the beautiful, crazy thing it was now. He'd only had the privilege of witnessing Sanji's unspoken avowal of his feelings for Zoro to Kuma on Thriller Bark, something he couldn't share with the others but cherished as a new friend.
And that's what Brook was: a friend. He'd been accepted not just as a crewmate, but as nakama. He couldn't have asked for anything better. They'd gifted him with unfettered acceptance and brought joy to his heart. He hoped that he would be with them a very long time.
(Not that he had a heart, because he was a skeleton! Yohohoho.)