The Point of Love Triangles
It's en vogue to hate on love triangles right now, and while a good deal of the criticism is deserved, I think people are missing the point of what a love triangle is meant for. A love triangle when used correctly is an extremely useful tool to show a character's growth, personality, and values.
The most important thing you can understand: a love triangle is the physical manifestation of a metaphysical crossroads and the focal character must make the choice. A question has been asked, and it must be answered. The focal character (the one everyone wants) can't go back to their old life, and now they're forced to make a decision on who they want to be going forward. The paths they can take (and the consequences of those paths) are shown by their love interests.
I'm going to illustrate with the classic love triangle: the new girl, the bad boy, and the good boy. Of course, it doesn't matter the genders of the characters or how many potential love interests there are, but this makes it easier to explain.
The New Girl (focal character) is thrown into a new world. The "New World" spectrum goes from literal (space travel/teleportation/pulled through time) to the figurative (new job/growing up/new school/rebuilding a broken life) with plenty of grey area in between (hidden secret society/new country/war). The New Girl is out of her depth and confused in this new world, and she's faced with dilemmas and decisions she'd never faced before. In a more life-focused world, this might mean choosing whether or not to play the power games everyone else in the office plays, choosing to leave a friend group she doesn't like or confront the others about what she doesn't like, choosing whether or not to go to parties where there are drugs and alcohol, choosing whether or not to stick up to a bully who is targeting her or someone else, choosing whether to follow her passion for the arts or the safe route of a stable job, etc. In a more action-oriented world, this might mean choosing whether or not she's willing to kill and for what, choosing to fight when she could choose to be safe, choosing forgiveness over revenge, choosing whether or not to use morally corrupt means to get power for what she thinks is a good cause, etc.
The two love interests should have contrasting answers to that question. This is why she can't choose between them: it's not that she isn't sure whose abs she likes more. She can't decide between them because she can't decide which answer is the right one. This does not mean that one of the love interests has to be evil/abusive.
The Bad Boy represents power. He doesn't follow the rules he doesn't want to, he's intense, he's persecuted by society, and he doesn't cave to social pressure. He wears his moral code on his sleeve, whether that's good or bad: he'll threaten violence on a bully, disrespect authority figures he thinks are wrong, and confidently advocate for what he wants. He puts his money where his mouth is and is willing to suffer for what he thinks is right, detention, write ups, physical pain. He wasn't just born this way: his strength comes from deep wounds and old hurt. He was weak once, and he knows the suffering that causes, and now he wants to keep anyone else from suffering the same way again. He doesn't just protect the New Girl, he empowers her. If the New Girl is being bullied, mistreated by an authority figure, forced to conform by her parents, wants to pursue a riskier life path, wants to protect people, or wants revenge, this attitude can look very attractive. Long term, though, this kind of personality can lead to difficulty getting/keeping a job, unnecessary trouble with authority figures, stubborn refusal to compromise/not realizing the other person feels railroaded, etc.
The Good Boy represents safety. He follows the regulations of society, he's laid back, he's diplomatic, and he's better attuned to how other people feel. Being law abiding doesn't mean he would follow bad rules, but he buttons his shirt, straightens his tie, and walks on the crosswalk only when the light says he can. He cares what people think and feel, and he tries to be something that they like. He can be susceptible to peer pressure, participating in activities he doesn't really like because he wants to make people happy, and bending the truth to avoid ruffling feathers. He also picks up on little things people like and remembers: he found out when New Girl's birthday is and brings her favorite coffee (he read her order on a receipt she dropped) and a cake pop (strawberry, to match the earrings she wears), he runs ahead to open doors for everyone (not just women/New Girl), he stays after a party to help clean up, and he's good at picking on things that bother people and steering the conversation away from those things. He's kind, stable, and sticks to what he knows works. If the New Girl struggles with anger issues or impulsivity, comes from a chaotic home life, wants peace and a steady life after the conflict, needs to learn forgiveness, or needs to learn to overcome a prejudice, the Good Boy shows what she could learn to be. He comes with downsides too, though: he avoids conflict, he can struggle to take a firm side because he can see both sides, he might value societal acceptance over defending the New Girl in a questionable decision, and his long-term goals might mean the main character would have to give up her wilder side.
Who the New Girl chooses isn't just her choosing a partner. It's her choosing a life and a set of values. This is why it's very important that she makes a choice. If you don't want her to end up with a love interest, keep in mind that rejecting both suitors will seem to the reader like she's rejecting both paths. Maybe she is rejecting both paths and forging her own path, but it will be hard to have her choose one of the two paths and but also reject the love interest who represents that path without undermining your message and her character arc.
Framing the whole love triangle around the moral ideals the characters represent makes plotting the whole story easier.
You know your New Girl needs to have a reason to like the Bad Boy, so she's persistently targeted by a bully and he not only defends her but builds her confidence and skill so she can defend herself.
You know your New Girl needs a reason to like the Good Boy, so he talks her out of trouble with an authority she offended and gives her a few tips on how to use tact and charm to her advantage.
You know you need a sweet scene with both, so you have Good Boy notice that she's been upset all day when no one else did, ask her about it when they're alone, let her be vulnerable, and comfort her.
For Bad Boy's sweet scene, she patches him up after he jumps into a fight to protect her, and when she says that she's not worth it and he shouldn't have gotten hurt just because she was too weak, he tells her that she is worth it and that she's stronger than she knows.
You need to show how both the love interests change her and how she changes them too.
New Girl in the beginning might harshly judge someone for their religion, social class, personality, or background because she's been mistreated by that person or by people like them before or because her side is in conflict with that side. After learning the value of gentleness and kindness from Good Boy, New Girl changes her mind and is kind/merciful to someone she previously disliked. After learning the value of protecting others, she defends that person from someone else.
New Girl might confront Bad Boy about how he hides his pain and feelings behind a mask of strength, which prompts him to share with her something he's never shared with anyone before: a secret passion like painting or music, fears he's always tried to hide, scars with a tragic background, etc.
New Girl might confront Good Boy when he chooses not to get involved in an argument she needs his backup in. He justifies himself by saying that he can do more good by staying in the good graces of the person she was arguing with, but she calls it cowardice. He takes this to heart and apologizes, and later does defend her in another confrontation.
If you want her to date both love interests before making a decision, you have her head a little ways down one path before coming to another crossroad and needing to decide whether to continue down that path or change her mind and go the other way.
For instance, she dates Good Boy, but when she goes to a high society party with him, she's disgusted by how fake everyone is and by the mask he puts on to blend in with them. New Girl has to decide if she values the connections and power that these social games can bring her or if she values living authentically at all times more.
Maybe she dates Bad Boy, but his rules don't apply to me attitude gets them both arrested and nearly charged with a crime. Worse, he doesn't seem to regret anything other than getting caught and starts planning to try the same thing again. New Girl has to decide if she wants to be someone who lives a truly high-risk life with the real consequences that could bring or if she wants to play things safer.
Maybe she dates both, breaks up with both, and then one or both of them makes a choice too. Remember, the focal character is a crossroads for the love interest too. Both of the love interests should change as people, not because "she can change him <3" but because they are dynamic characters just as capable of moral reflection and development as she is. Will the Bad Boy learn to deal with painful emotions with trying to hide behind anger? Will the Good Boy choose New Girl and the boldness she represents to him over social status with fake people?
Add more love interests so long as those love interests also represent their own moral choice
Replace either love interest with a friend (make the New Girl choose between one friend or another, make her choose between a love interest or a friend group, etc.)
Replace either love interest with a job
Replace either love interest with a parent (make the New Girl choose between the values/culture of her family and the values/culture of a love interest)
