"Because of my dad. I've been trying to find him. I just want to talk to him, to understand why he left. I've come close to finding him... I tracked him down last summer. But, um, he didn't want to see me, and he wrote me a letter explaining. He was with my mother." Nate gets why that's a problem, and thus why she dumped her mother halfway through Hudson Hero. "And I felt like, somehow... His letter meant something. You know? But the truth is, he knows who I am now, and he hasn't come to find me. I think talking to Elizabeth made me finally realize that he just... Doesn't want to be found." (Which I think is precisely as true as Elizabeth's entire story, which is to say: Entirely true, but also a total lie.)
Nate asks why she kept this from him, and she leans if possible even further into the pillar, and uses small words to explain that dating is fun, and Nate is fun, and fucking is awesome, and why mess that up? Last time she tried to be a grownup woman -- with the grownup version of Nate, note -- that turned out to really suck. So if she's rebounding with the guy destiny picked out for her, why rock the boat with her grownup problems? Nate says that dating is good, and Serena is good, and fucking until you break hotel furniture is awesome, but also that he's not quite the cretin that everybody thinks he is, and is actually a phenomenal boyfriend (which we know to be true and Jenny takes as an article of faith), so how about she treat him like a person? Serena's totally not sold on that, but smiles sweetly and says she wants them to be that person for each other. An option she had not considered. At least we burn trying.
So while Nate offers the opinion that maybe vdDubs just sort of sucks if he doesn't even want to know his awesome daughter -- verbatim what Carter Baizen told her approximately thirty-seven years ago in a wooded area, by the way, but we cut both Nate and Serena a lot of slack around here because they're doing as well as they can with what they have to work with, brainwise -- and they hug and are sweet, Elizabeth wraps up the story of how she was so uninterested in marrying Bart Bass that she cooked up a byzantine fake-death strategy which caused Chuck a lifetime of abuse so severe that he became a seer of ghosts and occasional rapist.