When looking at character types, the Love Interest occupies a relatively major role in most popular stories. From books like Mary Shelley's Frankenstein to more recent works like the video game Witcher 3: Wild Hunt you'll find there's generally one or two characters in a story that the main character is romantically interested in for one reason or another. While this may not be a central focus to the story (and in most cases really shouldn't be) it's a relevant piece to the construction of your story, and should be treated with respect as such.
The Love Interest is stereotypically less adept at whatever their potential partner's main strength is, whether that's combat, empathy, magic, or academics. This is at least partially because you can see a lot of real life relationships play out this way, where one person complements their partner's strengths, rather than competing with them. That said, there is plenty of precedent for the Love Interest to be just as good or better than the main character at what they do best - we'll cover more of this dynamic when we get to the Rival.
And with that, it's interesting to note that any of these character types can be blended, mixing the main characteristics of two or more types to reveal a unique relational dynamic. For an excellent example:
Gale Hawthorne, from The Hunger Games series, is a blend of the Love Interest and Best Friend character types. This gives the main character, Katniss, an established connection with him from the start, and affects their interactions throughout the series.
Alternately, you have Princess Leia, particularly as seen in Star Wars IV: A New Hope. She serves as both Love Interest and Rival to main character Luke, being more skilled/talented at pretty much everything practical (except for "being a Jedi").
These character roles are not only interesting to consider and to play with, but they are the underpinnings of the way your characters interact with one another. Consider, when installing a Love Interest in your story, how you want him or her to act with the other characters in the story, and what character role and relationship will best serve that purpose.
Who's your favorite Love Interest character?