You know one of the things I love about Sam Drake? It's the fact that he is childfree. His life is about traveling and adventure, it's about his career and aspirations.
Its a directly contrast to Nathan, where his end game being a wife and kids works wonderfully. He still loves his adventures and discoveries, but for him, whether or not he denied it in his younger years, he still craves a relationship and stability. I mean, he married Elena relatively soon after the first game when they met. The only reason he had such a difficult time commiting, was because of the instability of his life, and the world he had basically lived in since he was ten. But even then he still wanted Elena, still wanted to be her husband, and he still aspired for some kind of family and normalcy, whatever that meant for him. It's a beautiful progression from the first game to the fourth, I think. It just fits him.
With Sam, however, he just doesn't aspire for that. And sure some of his past might have had some influence, but it's more so just who he is. Marriage and making his own little family just isn't part of that, something you see when Sam and Nathan are talking about family and normalcy when they first get to Libertalia. Sam is comfortable being single until he finds someone he likes (which is common of course), and when he gets that special someone it doesn't involve marriage or children. It just the two of them, and Sam's adventures- whether or not his partner joins him. For Sam, the family lifestyle would really never work with him, and it would probably leave him more frustrated and disappointed with his life then anything else.
Though, I know for a fact he loves being an uncle. He visits his family after a job and when he first sees Cassie he loves her to the moon and back, though he wouldn't really babysit her for long (and Nate and Elena probably wouldn't want him to, let's be honest). He visits and brings her little trinkets from his adventure, little baubles and toys. He definitely gets a little scolding form Elena and Nate when he divulged too much of what happened the first time ("Sam, don't you dare tell her that you killed people!"). He would die for her, and he knows for a fact of anything was to happen, and she needs him? He could be in the middle of a damn jungle, and he would absolutely drop it if it meant protecting her (as he would with Nathan and Elena too, of courae).
He keeps busy, almost all the time, if he isn't on some big adventure he is on some small job. And if he isn't on a small job he is probably searching for one; big or small, or going on his own mini vacation, or visiting his family. So even when Cassie gets older, he isn't that keen on taking care of her, but he does a couple times. Nathan and Elena are a bit torn on how to feel when Cassie talks about knowing how to fight and defend herself after hanging out with Uncle Sam for a week, but he insists that she should know something, and they can't help but agree to a certain extent. Nathan helps teach her after that, and Sam jokingly brings up getting "Auntie Nadine" to help train her. Elena and Nathan aren't so torn on that one.
And Sam loves his life. Maybe he finds a significant other, and man, if they love traveling and adventure as much as he does he is just so in love. To him that's the dream. Traveling the world and finding amazing discoveries with the people he cares about; friends, family, a partner- the man couldn't ask for anything more.
