I think Finnick was killed off to show that war doesn't discriminate whether we love a character or not. Plus, it would have seemed odd if only minor characters died during the mission.
I think you have to go back to Catching Fire re. 'the triangle'. Katniss was prepared to let Gale go in her goodbye speech to him before she was whisked off to the Capitol for the Quarter Quell but she never got to make it as no goodbyes were allowed. Katniss had chosen Peeta by the end of CF (although she doesn't say it)but her reaction when Peeta almost dies, the beach scene and especially her behavior when Peeta is captured by the Capitol and is unable to function as MJ when she knows of his torture indicates that for Katniss, Peeta was the one. Gale put in a last ditch effort in MJ but was put off by Katniss' 'drunken' response and he also witnessed Katniss and Peeta start to grow close again during the mission to kill Snow. Finnick wasn't necessary re. the triangle. And I doubt the bomb was needed either as - it was the excuse rather than the reason.
I think you have to go back to Catching Fire re. 'the triangle'. Katniss was prepared to let Gale go in her goodbye speech to him before she was whisked off to the Capitol for the Quarter Quell but she never got to make it as no goodbyes were allowed. Katniss had chosen Peeta by the end of CF (although she doesn't say it)but her reaction when Peeta almost dies, the beach scene and especially her behavior when Peeta is captured by the Capitol and is unable to function as MJ when she knows of his torture indicates that for Katniss, Peeta was the one. Gale put in a last ditch effort in MJ but was put off by Katniss' 'drunken' response and he also witnessed Katniss and Peeta start to grow close again during the mission to kill Snow. Finnick wasn't necessary re. the triangle. And I doubt the bomb was needed either as - it was the excuse rather than the reason.