I guess we all remember this scene. Emma wants to find a way for David to leave the island and asks Hook for information about the Dreamshade and the magical water. She mentions his brother and that pisses him off, so he shuts her off - however, only when it comes to talking about Liam. Apart from that, he does offer what knowledge he has of the cure. But still the Liam thing is not to be touched upon.
Some episodes and many bonding moments later, Hook brings up the Liam thing himself.
Emma has just witnessed her own mother’s death while being unable to do anything to save her. This hits her so hard she doesn’t even realize it doesn’t make sense, since Emma is still there, existing. She’s obviously in need of comfort, of someone who understands what she’s going through. Hook does that by opening up his heart to her and talking to her about one of the most painful moments in his long life - something he’d shut her off from back then.
And may I say it surprises her.
She’s still not used to being put first. Much less used to someone putting themselves into an emotionally vulnerable position so that they can sympathize with her.
He deliberately let her into one of his saddest memories to help her feel better. Most importantly it looks like Emma herself understood how hard that must have been for him. If that’s not great friendship and understanding between two people who aren’t even a couple yet, I don’t know what it is.