The love triangle between Katniss, Gale, and Peeta is a major part of The Hunger Games franchise. There always appeared to be a spark between Katniss and her best friend, but when Katniss is reaped, everything changes. To survive, she's forced to fake a romance with Peeta, a boy who lives in her district.
But Katniss falls in love with Peeta for real and her friendship with Gale becomes strained. Katniss feels pressured to choose between the two and ends up picking Peeta. They get married, have kids, and live a long and peaceful life together after the rebellion. However, there are several reasons why being in a polyamorous relationship with both men would have also been a valid option.
Both: Katniss Wouldn't Have To Lose Anyone Else
Katniss is an incredibly selfless protagonist who only cares about keeping those around her safe. Before volunteering for the Hunger Games in her sister's place, she had already lost her father in a mining accident, and her mom was so far gone with grief it was almost as though she lost her too. If Katniss picked between Peeta and Gale, the other might decide not to be in her life anymore. If Katniss were with both, she wouldn't have to say goodbye to one more person she loves.
Choose: Gale Didn't Seem To Like Peeta
Gale never seemed to be a big fan of Peeta, even though Peeta was a genuinely kind person, so his dislike can only be attributed to Peeta's relationship with Katniss. Whether he's talking about Peeta or talking to him, Gale almost always uses a tone of disdain. The only reason he puts up with him is that he cares about Katniss and knows that Peeta is important to her. The relationship might not work well if Gale's negative attitude towards Peeta gets in the way.
Both: No One Would End Up Heartbroken
In The Hunger Games, hearts are broken left and right. Everyone ends up losing people that they love, but in this trio's case, they have a chance to keep everyone happy.
Neither Gale nor Peeta has anyone else in their lives besides Katniss. Peeta even admitted that without Katniss there would be no one left that he cares about. Choosing between the two of them would leave one completely alone when, instead, they could all have each other.
Choose: Peeta And Katniss Had To Sell Their Traditional Romance To Survive
A huge part of the plot involved Katniss and Peeta broadcasting their fake romance to the world. They had to convince viewers of their love story in order to gain sponsors and survive in the arena. It would be difficult to balance a relationship with both Peeta and Gale while competing in the Hunger Games twice. Snow always has Katniss on his radar and even records video footage of her kissing Gale when she's supposed to be with Peeta. The people in the Capitol are closed-minded, and it would be hard to sell three star-crossed lovers when one of them isn't in the games.
Both: They Were All Better Together
Katniss, Peeta, and Gale are the definition of a dream team. If they're working together, there's almost nothing they can't accomplish. If they decided to be in a polyamorous relationship, rather than be constantly on edge waiting for Katniss to make a choice, they would be able to put aside their differences and focus on the task at hand. All three characters have their strengths, and it could be the exact dynamic that everyone needs.
Choose: Gale Probably Wouldn't Be Open To It
Gale would likely be the biggest roadblock in a polyamorous relationship. He was constantly pressuring Katniss to choose between the two of them, and he was clearly unhappy when Katniss was unofficially carrying something on with both.
Peeta loves Katniss so much, that it's hard to believe he wouldn't be on board with this solution. If there was a way for him to be with her without anyone else getting hurt, Peeta would have done it.
Both: Gale And Peeta Could Have Formed A Connection
Just because Gale and Peeta didn't get along doesn't mean they couldn't have. They're both courageous people and the only reason there was animosity between them is because of their mutual love for Katniss. In this arrangement, they could get to know each other on a more personal level, and it's likely that they would end up becoming close.
Choose: Katniss Had Trouble Being Around Gale After Prim Died
Although it's unclear whether or not he's directly responsible, one of Gale's bombs killed Prim when she was treating the injured during the rebellion. Gale didn't mean to hurt her, but his actions did have consequences that Katniss was unable to see past. It's a complicated situation and although we didn't see much of his reaction, it's only fair to assume that Gale felt horrible about what happened. However, Gale no longer felt like a safe place to Katniss and was instead a constant reminder of her sister's tragic death.
Both: Their Relationship Could Have A Positive Impact On The Public
Katniss was known as the "darling of the Capitol" and many people who saw her on television started to follow her lead. Because of the huge impact she had on the districts, she was single-handily responsible for the start of the uprising. The Capitol is full of judgmental and impudent people who are stuck in their old-world views. If Katniss, Peeta, and Gale were in a polyamorous relationship after the rebellion, they could help make the world a more accepting place.
Choose: Katniss Never Loved Gale The Same Way She Loved Peeta
When it comes down to it, it's painfully obvious that Katniss never loved Gale like she loved Peeta. Gale was her best friend, but Peeta kept Katniss grounded. Peeta's pure heart and selfless nature made Katniss in awe of him, and he was like a beacon of light in the dark. While she could be in a relationship with both, her love for Peeta was so overpowering Katniss might not even want to do it. Gale said, himself, that Katniss only ever kissed him when he was sad. It would be difficult to let go of her best friend, but it's clear where Katniss's heart lies.