Talk to your table
This is basically the generic solution for all problem-players and group-dynamics problems. I'll break it down following my own experiences with a similar situation.
In my case, I was in a game with player who was a little bit too triggerhappy with PvP (in a D&D 5e game) for my taste. I'll recount the steps I took to address the situation. In my case, the game was very large at 11 players, so your mileage may vary when applying this solution to a smaller group.
Step 1: Sort through your own feelings
Everything else you're going to have to do here involves talking to people. Communication is hard, so it's important to be able to clearly articulate your feelings and reasons. For me, it's way easier to do that ahead of time.
Figure out what your bottom line is - would you leave the group if nothing changed? If so, how much would need to change before you'd stay?
In my case, the player himself was fine, but I didn't like how much PvP was going on, and I felt like I was picking up the pieces after every time things devolved into PvP, making concessions and trying to find ways to avoid splitting the party permanently. I would have been fine with an agreement to either cut back on the PvP or if everyone agreed that kicking characters out of the party was an acceptable solution for in-character antisocial behavior.
Step 2: Find out how the other players (and GM) feel
In my case, there were some members of the group that I was more comfortable approaching than others. I approached these players privately and talked about the game, and how they felt things were going. The intention here is not to try to rally support to your cause, but to determine if that support already exists.
If the problem player (or that player's playstyle) is a bad fit for the group, you will do yourself and the group no favors by leaving.
In my case, while some of them shared my concerns with the problem player, I also learned that a handful of them had very different problems with very different players. Players who I thought were fine had been banned from groups with other players. Furthermore, many of them enjoyed the high-PvP style but also didn't want to split the party because that would make more work for the DM (who was time-limited due to pursuing a very intensive degree which left him very little time to prep or run the game).
Step 3-a: If you believe change is possible, hold a meeting to discuss it
At the meeting, confront the player in question, and inform them that you and several others have a problem with their behavior. Formally propose the changes you decided you needed in Step 1, and found support for in Step 2. Discuss them.
You may not get everything you want. That's fine. The point here is not to convince your friends to play your way - the point is to agree on what is and is not acceptable behavior at the table.
In my case, I didn't have the group behind me, so I went to step 3-b instead.
Step 3-b: If you do not believe change is possible, leave.
Be polite - try to leave on good terms with any players whom you might want to interact with (either in another game or in life) in the future.
In my case, I said that I was burned out and wanted to get the timeslot back. I later created a new game with some of my closer friends from the same group.
Step 4: Determine if the game is worth playing again
Play for a session or two after the big meeting, and see if you're having fun now. If you are, problem solved. If you are not, go back to step 1.