There's a difference between good storytelling that leaves some gaps to the imagination and lazy storytelling full of plotholes. Elena and Nate's relationship or Nate and Sully's relationship is the former. The actual plot of UC3 is mostly the latter.
The writing and acting with the three main characters conveys very well what it's supposed to. Yes, they got married after 2. Nate left to chase after more treasure, because his priority was always the adventure. The ring conversation. The nap conversation. It all says what it has to without being bloated exposition. It also helps that this is something that you see even in the gap between 1 and 2. They weren't looking like they were gonna get married or anything at the end of 1, but the romance interest was there. They meet again in 2, and you can tell they haven't seen each other in a long while and stuff is awkward between them. Then you see Chloe and Elena sizing each other up, etc. It's all a continuity, and it works. This is the one thing that ND handles for realz better than any other gaming franchise. The character interactions.
The tarot card? The shipyard? Why Marlowe wants this hallucinogen beyond "Oh, I'm part of a secret society and it's supposed to be ours"? Why Talbot can seemingly control minds? What's up with the spiders? This is not stuff where there's continuity helping us fill in the gaps. This isn't character interactions, where often leaving stuff unsaid says just as much as actually saying it. Yeah, you can fill in the gaps with any number of possible theories. You can brush it off as adventure tropes. (And to be fair, it usually doesn't bother me as much. There's just SO MUCH of it in this game that it actively works against my suspension of disbelief.) But it's so, so not the same kind of "gap." They're not conveying anything by implication. They're just being lazy in connecting the dots.