That is perhaps the current convention in action pictures, but has not been the case in the past. In 40s films, for example, the Obstacle/Love interest is often the Guardian, or even the Reason archetype.Perhaps the one thing that IS rather consistent is that the Love Interest (if there is one) is often the Obstacle, regardless of the objective role, archetypal or complex. Still, in Star Wars, Obi is the obstacle, but Leia is something of the Love Interest.
That is one reason that thinking about Heroes, Villains, and Love Interests is much too indelicate to describe what is really happening in stories. Though certain combinations may come in and out of Vogue (such as the anti-heroes of the late sixties and early seventies) thinking in conventional terms is contrary to coming up with unique combinations of one’s own that elevate a story as being not quite like anything else.
One final note: In “Aliens” the Archetypal role of Guardian is split between the Michael Biehn part and the Paul Burke part, each getting half of the Guardian characteristics and half of the Contagonist characteristics.. Biehn is Help from the Guardian, but Temptation (“Nuke them from orbit” – which will never make Ripley face her fear) from the Contagonist, whereas Burke is Hinder from the Contagonist but Conscience (“You gotta get back on the horse!” – which is just what she really needs to do) from the Guardian.
In short, there are no right or wrong combinations, just commonly used conventions which on the positive side are immediately recognizable by the audience, yet on the negative side are predictable and pedestrian.
Although designed to create much more rich and complex characters, Dramatica also defines eight archetypes, each of which represents a broad aspect of our own minds when attempting to solve a problem. These archetypes are: Protagonist (the drive toward the achievement of something positive), Antagonist (the drive toward the achievement of something negative), Guardian (our conscience), Contagonist (our temptation ), Reason (our intellect), Emotion (our feelings), Sidekick (our faith), Skeptic (our disbelief).
Subjective Characters: Main and Obstacle.
Dramatica divides characters into two types – those seen in terms of their dramatic functions (Objective Characters) and those providing the audience with a passionate involvement in the story (Subjective Characters). The Objective characters are most broadly identified as the eight archetypes listed above. The Subjective characters are primarily represented by the Main character and the Obstacle character.The Main Character represents the audience position in the story, as if the story were happening to the audience members themselves. The Obstacle character has the most personal effect upon the Main Character, pressuring the Main Character to change his or her world view and see or do things differently. Just as the Protagonist and Antagonist objective archetypes clash over practical matters of achievement, the Main and Obstacle clash over personal matters that define who one really is and what one will become.
Though quite separate in concept, the functions of an Objective Character and the “involvement factor” of a Subjective Character are often combined in the same “player” in a story.