I've had a remarkably similar problem to this, and it's a tough nut to crack.
First, discuss this (privately) with the other players and the DM, because any solution needs to be motivated by more than you. If either the DM or the majority of players also feels this is unacceptable, then you can deal with it. If everyone else doesn't care, or doesn't care enough to force the issue, drop it.
Assuming there is consensus to act, I'd propose the following approach.
Talk to the player, and say the following, roughly.
"I appreciate that you've made a character that fits your concept, and are roleplaying accordingly, but you've made a character that can't function in an adventuring party. Right now, I can't roleplay MY character effectively (nor can the rest of the group), because my character (and the other characters) would never travel with your character. However, since as players, we're in the same game, if we were to do that, it would be effectively asking you, as a player, to leave the game. So please understand that if you don't compromise your roleplaying concept of a dagger throwing non-healing non-defending paladin, we will no longer compromise our roleplaying concepts of adventurers who don't share treasure with people who we don't see as helping us achieve our goals."
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gnfnrf