In the movie, Felix is smitten by Calhoun at the first sight of her, and flirts with her throughout the course of the story. At first, Calhoun doesn't return his affections, because every time Felix expresses his feelings, she is reminded of her fiance who was killed by a cy-bug on their wedding day. However, after spending much time together in the movie, Calhoun eventually returns his feelings and they share a kiss. At the end of the movie, the two are married.
Within the RotBTD fandom, this pairing is not usually mentioned. However, in some fanfics, the two appear as a married couple or as boyfriend/girlfriend, though they are often used as background or supporting characters.
Note: Please add only ones that are part of the RotBTD fandom