If you make romance games, there's an interesting GDC talk on YouTube about exactly that. It's not like groundbreaking new advice exactly, but more like practical advice on how to write more interesting romance without too much extra effort.
tl;dr: Think why your characters would have chemistry and how they would react to things that get them excited. Then build your gameplay or choices around those things, I guess.
My approach so far has been more or less that the protagonist and the romance interest just fool around together and grow to love each other. And, well, that actually sort of falls under what the video suggests, I guess, but sadly it doesn't quite work in case of the Next Big Thing. The tone of the game is a little bit too serious for fooling around a lot.
Some of the ideas later in the video could work, though. Things like making the reactions of the romance interest hard to read and maybe even throwing slight randomness to the mix. You know, not because I want to make the game particularly hard to win, but...
