Did Gale mean to kill Prim? No, Gale did not mean to kill prim but he still designed the bomb. But, although he holds a small fraction of responsibility, he never meant for Prim to get hurt.
Before the Capitol battle, Gale had explained to Katniss his series of bombs designed to feed off human compassion: a small bomb would go off, and then when medical aid rushed in, a second bomb would go off, killing those people as well. Incidentally, it's this exact type of bomb that took Prim's life.
Prim was the most important person to Katniss throughout the whole series, so much so that she sacraficed herself for her. She was Katniss's connection to compassion and empathy. Killing her was showing that even after everything, Katniss couldn't have everything she wanted.
Though the rebels would go on to win against tyrannical President Snow and the Capitol, Gale's thirst for violent revenge seemed to sever any chance he had with Katniss: Mockingjay insinuated that Katniss' younger sister Primrose was inadvertently killed by a firebomb when working as a medic.
In Mockingjay, Katniss defied Gale's wishes when he was captured because she didn't want to see him dead. It seems like a nice thing for her to do, especially since Gale is soon able to escape out of the Peacekeepers' grasp because of the rebellion's "distraction".
Although she will never know for sure, Katniss does recognize that she cannot be with Gale. She will never be able to forgive him for his idea — the parachute bombs — that killed Prim.
Katniss's focus on survival and her family's safety prevented her from fully considering romance, but her feelings for Peeta and Gale diverged in the end. Katniss ultimately chose Peeta because he understood her trauma and she didn't want to lose him, proving her love for him.
Peeta, Annie, and Beetee vote no, while Johanna and Enobaria vote yes. After some thought, Katniss demands to kill Snow. Once she receives an agreement, she votes yes, for Prim. Realizing something is up (as Katniss would never do that), Haymitch votes yes, too.
Katniss feels betrayed, most of all by Haymitch, who used her and Peeta. Eventually she wakes to find Gale there. He's badly injured and tells her the Capitol bombed District 12 after the Games. He got Prim and Katniss's mother out in time, but the District 12 is gone.
Katniss comes close to crying, something she knows she mustn't do because it would indicate weakness to the other tributes and make her look vulnerable; thankfully, Haymitch distracts the crowd and the cameras by stumbling off stage.
Gale was responsible for creating weapons that would trigger a second wave of bombs to target first responders and combat healers. This invention potentially ended up killing Prim, but even if he wasn't directly responsible, Katniss found this tactic so abhorrent that she lost her affection for him.
While Prim is caring for the wounded, a second set of bombs go off, killing her, along with everyone around her. This act of treachery and shameless targeting of the innocent is what finally turns President Snow's guards against him. They believe he is to blame, when in reality, Alma Coin was responsible.
The double bomb that kills Katniss Everdeen's sister, Primrose, was designed by two rebels: Beetee and Gale, Katniss's lifelong friend. Previously, Gale had explained that the double bombs are designed to appeal to mankind's weakness for compassion.
After Prim's death, Gale leaves voluntarily because neither of them can avoid the matter of Prim's death having been caused by Gale's invention, with Katniss letting him go without a word. Katniss subsequently grows back together with Peeta, whom she finds she loves again now that he is recovered from his hijacking.
Gale was trying to win, and he had no idea that Prim would be there. If I recall, he was extremely upset when he found out. Remember, Gale helped keep Prim alive her whole life, even when Katniss was in the games.
Snow laughs after Katniss killed Coin because he enjoys the irony of the situation. He avoided the official execution ceremony, even though Panem's citizens still take their revenge on him, while Katniss ends up snatching away the victory and power that Coin thinks she has successfully secured.
His feelings and memories are distorted with hallucinogenic tracker jacker venom, in a mind-control technique known as "Hijacking." The Capitol uses this method to turn Peeta against Katniss, making him believe that she is not only responsible for the death of his family, friends and the destruction of District 12, but ...
Peeta decides, though, that he will go out on his own to act as a diversion in case Katniss and the others need it. Gale gives Peeta his nightlock pill in case Peeta's captured. They leave early in the morning, bundled up and styled by Tigris. Cressida and Pollux go first, leading the way to the City Circle.
So when he said 'I'm with the Mockingjay' it meant that he trusted that the Mockingjay (as the face of the rebellion) would do the right thing for the cause they had both fought for.
In the 75th Hunger Games, Finnick Odair from District 4 had a token that was a gold bangle with a flame pattern. This token was first given to Haymitch Abernathy from Effie Trinket as a sign of them being a team. Haymitch gave it to Finnick to tell Katniss to make him an ally, as he could later help her in the games.
Gale does not marry anyone in The Hunger Games. He and Katniss talk about running away together and starting a new life in the wilderness, but they never officially marry.
It's only implied that they get it on via snuggling and other affectionate acts in close quarters — but if you have read the book, they really imply that they took their relationship to the next level.
When Katniss comes home to District 12, Gale immediately confesses his love for Katniss, and she realizes she might have feelings for him, too — but she can't explore them, because she has to continue her fake relationship with Peeta or else her entire family, including “cousin Gale,” will be killed.
