There’s so much tension between Sam and Nate that I didn’t pick up on the first time I played through Uncharted 4. Every interaction they have after the fight with Elena and Sully (and even some conversations before that) are packed with double meaning and things left unsaid.
Sam wants so desperately for Nate not to be angry that he’ll do anything–except apologise and tell him the truth. He makes cute small talk, reminisces about the old days, and tries to distract his brother with tiny things like climbing competitions. He even tries to spin the situation around and get angry with Nate (“why aren’t you enjoying this/I put so much on the line for this” etc) so that he can justify to himself for feeling guilty when he sees that sucking up isn’t working. It’s a lovely parallel to them as kids when Nate says that Sam only does nice stuff like show off motorcycles and gifts to make up for something he’s done or about to do.
Sam’s line to Nate in Chapter 12 (“She will get over it–I mean we bring back a treasure like that, anyone would”) not only demonstrates that he completely misses the point of why Nate and Elena fought, but that he’s also using Nate’s marriage to spin the adventure in his own favour - “if we find Avery’s treasure she’ll forgive you, so we have to do this now.” He can see that he’s losing his brother on the importance of this expedition, and he cannot tell Nate the truth and apologise now, so he uses Elena–who he’s come to realise is the most important person in Nate’s life–to persuade his brother into staying.
There’s a lot of bitterness in that too, because now Sam not only feels like he has to compete with Sully for Nate’s loyalty and love, but Elena’s as well, and he knows he won’t win. Nate’s already done the alienating (which Sam tried to do earlier with Sully at the Rossi Estate - “we can’t trust him/what if he grabs the cross for himself” etc), so now he’s left with using the excuse of repairing those relationships to motivate his brother to find Avery’s stash.
The more I play the game/rewatch the cutscenes, the more I pick up on how manipulative he’s being. This kid has mastered the art of getting what he wants from people, and it’s amazing how much nuance Naughty Dog has packed into every part of this game.