[MENTION=6862394]LordShikamaru[/MENTION] My apologies, I know this might not be what you're looking for, but perhaps rather than plan machinations with your DM to kill a player that did something that was out of line, wouldn't it make more sense that the act caused this player's paladin character to break his oath?
Yes, your character was plotting and playing with forces that risked letting loose an evil upon the world. But perhaps from the perspective of the paladin's deity, your intentions were noble. And the paladin, being a friend and commrade, rather than take the more difficult road of talking to you, attempting to dissuade you from your course of action, or find a way to redeem you (ya know, standard paladin type things) he just straight up murders you.
To me, that is equivalent to a man discovering his brother is planning to commit a crime, and rather than try to talk him out of it or help him not do it, just figures "Eh, why bother. He's evil now. It's his time to go anyways" and kills him. That is really against what paladins stand for, from my perspective. This other player losing access to his oath, paladin powers, and having to atone for his own sins should maybe have been the focus, rather than a player and DM colluding to kill off someone's character.