Finn and Flame Princess actually did become a real couple in the show, infact it was the first and only couple in that involved Finn and was official. The two of them seemed to have been a great couple for them and fans went crazy over them. It was all going perfectly until he broke up with her in the episode "Frost and Fire" and in the episode "Earth and Water," Flame Princess took over the Fire Kingdom instead of getting back together with Finn, but she said they could still be friends. In episodes such as "Too Old", "Heartburn," "Love Games," and "Dungeon Train" Finn is still missing Flame Princess and can't get over her, and it is unknown what her feelings are or if they'll get back together.
As soon as Finn and Flame Princess happened, fans went crazy over their relationship. Many people have made fan art of them and people have voted their relationship better than Finn and Princess Bubblegum. Several Fanfictions revolving around their love are made almost every day. The episode "Burning Low" which is the first episode to officially confirm them in a relatinship has made itself the most viewed episode of Adventure Time ever and is still getting more views. Ever since that episode, Adventure Time has gained more fans and polularity and they all have been waiting for more episodes with Flame Princess. In the episode "Frost and Fire" Finn and Flame Princess broke up and many fans have felt depressed about this. They all want Finn to get back together with Flame Princess again and one of them has even written a fanfiction where they did called "Fire & Light."