Here is all you need to know:
Zoro jealous towards Luffy speech about Sanji

:zorothink:
Zoro worried about Sanji and Luffy acknowledging Sanji's potential and that these 3 would do the same thing on that situation
That irrational faith on Luffy when apparently there is nothing much left to do

Zoro and Sanji acknowledging each other early post-timeskip, but thats just when they aren't together
The way people see them towards very especific situations
The most cool is that this was kinda introduced since Baratie arc, that arc is very focused on Luffy, Zoro and Sanji and how they want to live their lives, there is when Luffy shows some moments of reckless willpower, about not holding back even it it means death, Mihawk easily defeats Zoro then Zoro establish his biggest goal to achieve once for all, with Luffy and Zoro witnessing this event as something special.
In my point of view Sanji realizes he is much more like Luffy and Zoro than he actually thought he was and he just needed to step up.