Zoro was in love with Sanji. He had been for a long time, ever since the idiot cook had saved Luffy in Arlong Park. Sanji hadn't known Luffy for long back then, and yet he'd risked his life to save Luffy from drowning. Zoro had fallen hard and fast for that man and his love had only gotten deeper over time.
Sanji didn't know it, though. Zoro hadn't told him, and he wasn't planning on doing it anytime soon. Or possibly at all. The crew was relying on Zoro to help fulfill their dreams. Zoro couldn't do that if he were in a relationship. He was worried enough for the others as it was, willing to sacrifice everything for them. He refused to put Sanji in a position of mourning a lover, which was bound to be worse than losing a crewmate.
Sanji hated Zoro anyway, so it wasn't as if Zoro was losing out on anything by not confessing. Zoro contented himself with being by Sanji's side, even though he'd inevitably get kicked in the head.
Zoro was in love with Sanji. He had been for a long time, ever since Sanji had rescued Luffy in Arlong Park. Sanji had barely known the crew back then, and yet he'd risked his life to save a drowning Luffy. Zoro had fallen hard and fast, and had loved him from then onward.
Sanji knew it. Zoro hadn't told him, and might not tell him anytime soon. Or possibly at all. Sanji understood why. Zoro's loyalty to the others, his devotion with helping them reach their dreams, meant that he'd willingly sacrifice himself - and had done so - to save anyone on the crew. Sanji knew Zoro wouldn't want to put any one person over another, and he wouldn't want to be the source of pain. Zoro didn't realize that the grief would feel the same.
Sanji loved Zoro anyway, even though he was losing out on a lot by not confessing. Sanji made sure to kick Zoro repeatedly in the head whenever he was near, for his stupidity.
Zoro was in love with Sanji. He had been for a long time, ever since Sanji had rescued Luffy back in Arlong Park when they were fighting for Nami. Sanji was nakama even before he knew it himself, and Zoro had been in love with Sanji since then.
Sanji knew Zoro was in love with him, even though Zoro hadn't said anything. Zoro thought nakama came first, but he could be a nakama and be in love, too. He didn't have to choose one or the other. They were all going to reach their dreams together, no matter what.
Besides, Sanji loved Zoro, too. Sanji had been in love with Zoro ever since Zoro had tried to cut off his ankles to save Nami and Vivi from Mr. 3's really bad tasting cake. Nami said Sanji told Zoro every time he kicked Zoro in the head, but Zoro was too much of an idiot to understand.
Luffy got it, though. And after he'd learned from Brook what happened with Kumo on Thriller Bark, Luffy sneaked into the infirmary while Chopper was helping Robin. Bandages wrapped around Zoro and around the bed, preventing Zoro from moving. Luffy popped Zoro's snore snot bubble, causing him to wake up.
"Hey, Zoro, you need to tell Sanji that you love him," Luffy said, without preamble.
Sleep left Zoro in a hurry. "What- how- no, I don't."
"Yes, you do," Luffy said. "Sanji keeps saying it with his kicks, but you don't tell him back. I want my nakama to be happy."
"I...," Zoro struggled for what to say. "I can't."
"You can't? Do you want me to tell him for you?" Luffy said. He turned and yelled toward the galley door. "Oi! Sanji!"
"Luffy! Don't--" Zoro started to shut him up, but it was too late. Sanji opened the door between the galley and the infirmary. A towel was flung over Sanji's shoulder and his sleeves were rolled up. Tiny soap bubbles clung to the fine blonde hair on his arms.
"What is it, Luffy?" Sanji asked, barely sparing Zoro a glance.
"Zoro loves you," Luffy declared. Zoro cringed and reddened.
Sanji puffed on the cigarette between his lips. "I know."
"Wait- what? You know?" Zoro stared at Sanji in surprise.
"Of course I know, you idiot," Sanji said.
"Why didn't you say anything?"
Sanji gave Zoro a pointed look. "You don't want that kind of relationship."
Zoro appeared chagrined. Luffy patted Zoro on a bandaged shoulder. "It's okay, Zoro. You're still nakama even if you're in love."
Zoro sputtered. Sanji smirked. Luffy clapped his hands together. "Sanji, give me meat!"
"I believe I have some leftovers that you can have," Sanji said, heading back into the galley.
"Yay, meat!" Luffy cheered. He followed Sanji, closing the door and leaving a staggered Zoro behind.
Zoro was in love with Sanji. He had been for a long time, probably from the moment they'd met. Sanji fell in love with Zoro not too long after that. Now they were together, and nothing really changed but the long periods of silence when Sanji and Zoro disappeared into the hold.
Sanji still kicked Zoro in the head. Only now when he did it, Zoro smiled.