Love interest and internal conflict
Question: The main characters of my novel have feelings for each other and I know that I want internal conflict to play a big role, but is a love interest really an internal conflict?Answer:
A love interest very often becomes the impact character -- the character who provides the main character with an example of a different approach, a different perspective or way of dealing with problems.
The impact character creates internal conflict for the main character by causing the main character to doubt or question his/her approach. The main character has to think about whose approach is better and whether they should perhaps switch to the impact character's approach. This is especially true around the crisis when the main character feels a lot of pressure to make the right choice.
At the same time, the progress of the relationship can also have an influence on the main character. The main and impact characters often share a certain perspective that sets them apart from everyone else in the story world and creates a bond between them. In a story where the two end up together in the end, there is usually a "black moment" in act 3 (of 4 acts) where it looks like their relationship is over. This can also force the main character to reconsider carefully what the right choice to make is.
It's true that people will often feel an internal conflict that seems to be just about them, but often this is the result of conflicting values they have learned throughout their lives, usually from other people.
It would be hard to illustrate all the influences on a person in a novel without turning the story into one long flashback or internal monologue. That might work in literary fiction, if the style and voice are interesting, but not in genres where readers want a plot.
In genre fiction, it's much easier to externalize the source of a main character's inner conflict by providing an impact character. A love interest is a good choice for impact character because they are someone the main character will listen to. Of course, another character can serve as well -- a friend, mentor, rival, etc.