So after reading a long conversation about Gandalf being an epic level fighter, it has been brought to my attention that Boromir was killed not as a plot device, but because he was getting too close to the DM's girlfriend. The facts are quite obvious for all to see, those in the gaming community have seen it far too often. One PC gets all the DM's favoritism, the closer they are to the DM the more good stuff they get. Poor Boromir got too close to Frodo, so he had to die.
It's apparent Frodo is being played by the DM's girlfriend. All the signs of favoritism are there. Frodo gets picked to be the Chosen One. At level one he's given not just the epic level artifact, but on top of it all he even gets gifted a substantial amount of money in Bilbo's house. So he's now the heir to Bilbo's fortune, who was obviously the DM's old character. After that it's all about Frodo, the Nazgul at the watchtower attack only him, causing drama centered on Frodo as he's rushed to the elves. Once there he's immediately gifted magic armor and weapons by the DM's old character. In Moria he gets a get out of death free card when the DM suddenly remembers that mithril chain would somehow absorb all the force of the troll's spear, where anybody else would have crushed ribs as well. In the final fight, not one Uruk Hai finds and attacks Frodo, despite the rest of the party being swarmed by them.
Now look at poor Boromir. Boromir was the nicest one to Frodo. When Gandalf forgets just because he's a high level fighter with tons of hit points and can survive climbing a mountain without assistance, Boromir points out Frodo's freezing to death. When Gandalf falls to what seems to be his death, again Boromir is there for the Frodo. When Frodo is grieving heavily outside Moria the taskmaster Aragorn wants to keep the party moving to the next encounter, but Boromir wants to give Frodo's player time to roleplay her grief. Finally the DM's had enough. Boromir has to die. The signs start almost immediately. When Galadriel gives out gifts most of the party gets magical weapons or artifacts. Boromir gets a belt. Not even a magical one. Not even important enough to be included in the movie. Sure Gimli gets only three hairs, BUT THAT'S WHAT HE ASKS FOR. Every other member of the party without a magic weapon gets one, except Sam who gets a magic rope which comes in quite useful not to far into the story.
So the party gets to Amon Hen, that's when it all comes to a head. Clearly the DM has been talking to his girlfriend because Frodo is suddenly hostile to Boromir, who has been nothing but supportive this entire adventure and been the shoulder to cry on. When the Uruk Hai finally attack, look at how the monsters are paired against the heroes. About half a dozen each head for Aragorn, Legolas and Gimli, while a full three dozen at least make a bee line for Boromir, Merry and Pippin while none go after Frodo and Sam. You've got at least five dozen Uruk Hai and you give two members of the party a pass in the big fight? That reeks of favoritism. So you've got Boromir facing down forty fighting Uruk Hai with Merry and Pippin along side him. Except none of the Uruk Hai go after the hobbits, they all concentrate on Boromir. The hobbits have to forcibly engage the Uruk Hai because none are attacking them, despite taking fire from the hobbits. No, every single one of them go for Boromir. When Boromir wipes out the entire first wave, he blows his horn to let the others know his situation. This also draw all the other Uruk Hai, which for some reason don't attack Aragorn unless he attacks first. All them go straight for Boromir. Finally after Boromir has completely exhausting himself killing more Uruk Hai than the rest of the party combined, then the boss shows up and easily takes down Boromir as he's low on hit points by this time. Seriously Lurtz? Three straight confirmed criticals? Not suspicious at all.
Once Boromir is down, Lurtz can't hit Aragorn to save his life. Every attack either misses or Aragorn shakes off easily. The fight takes just long enough for Boromir to bleed out, as Gimli and Legolas are still nowhere to be seen. So the DM gets his wish and kills off the character of the one guy that was nice to the DM's girlfriend. The DM then makes sure nobody else will get a chance to be the next Boromir by sending Sam and Frodo off on a side quest, far away from the rest of the party. Boromir's player quits the game in disgust and the party splinters into three groups. The DM made his life so much more difficult out of sheer jealousy.