Nate could be a great addition. He could be a confidant to either Chuck or Blair, and his own storylines could intersect with their married life. For example, if he gets into a business deal that affects Chuck and Blair's business.
It depends on how you interpret the story. Some might think they do, as there are hints of a possible reunion. But others could see it differently based on their own understanding of the characters' emotions and circumstances.
For a Chuck and Blair fanfic to be the best, it needs a compelling plot. It could be about them facing external threats to their relationship, like family interference or social scandals. Also, the dialogue should be on point, sounding like something they would actually say in the show. The chemistry between them in the fanfic should be palpable, just like in the original series. A fanfic that can make you feel their love, anger, and longing is a great one.
I'm not sure who Chuck Blair is specifically. There could be many people named Chuck Blair. Maybe he's an ordinary person with a personal love story that only his close friends and family know about. Without more context, it's difficult to tell the exact love story.
The fate of Quill and Gamora's relationship in the comics is quite unpredictable. They may or may not get back together depending on the creative direction of the writers and the demands of the story.
Zuko and Mai do get back together in the comics. The plot developments and character growth lead to their reconciliation and a fresh start for their relationship.
In the comics, Betty and Jughead's relationship is complex. Sometimes they do reunite, but it often involves resolving personal issues and external conflicts that test their bond.
One popular 'Chuck and Blair baby fanfic' might be one where the baby brings them closer together as a couple. Maybe it shows how they navigate parenting in the Upper East Side drama-filled world.