But it isn't a completely internal matter for PC 1 the moment he tries to role-play it out with PC 2.
What is at issue here is player 1's ability to decide on his motivations. His actions are always up to him too. Telling the other pc he's romantically interested
isn't even really part of the original scenario. Still, I'll chew this one over for you. The answer is the same. PC 1 can say or do what he likes in game as long as he is willing to face the in-game consequences.
Honestly, what it all boils down to is- for my table, anyway- it is completely ridiculous to try to place your character "above" or "outside" of the campaign setting and the events of it, which include betrayal, death, murder and yes, romance. I would no more make PC 1 untouchable by romance than I would by evil cultists ("I'm uncomfortable with non-Christian religions in game), demons and devils ("I'm uncomfortable with the existence of Satanic imagery in game"), spiders ("I'm an arachnaphobe, and I'm uncomfortable with giant spider attacks") or any other element.
If any of those are deal-breakers, by all means,
leave the table. Quit the game. It's not for me to force you into an uncomfortable game, but neither is it for you to dictate how other players play their characters.
For example: if player 1 (player, not character) is physically touching Player 2 in any why that makes player 2 uncomfortable, it is okay to say so, right then and there, and it is probably best to do so.
But now you're stepping way outside of the parameters of the discussion. Has anyone argued that it's okay if:
-One player tries to molest another?
-One player tries to beat up another?
-One player tries to force another to eat or drink his favorite snack?
We are quite clearly talking about an entirely different matter here because, instead of it being the actions of
characters that are in question, it's the actions of the
players that are in question.
Put another way, while I wouldn't let one player stop another pc from having a background that included mass murder, I wouldn't want a mass murderer as one of my players. (And a smart group of pcs will
not recruit pcs unsuitable to their party. If someone insists on making a character that won't fit in, the
characters handle it- and ultimately, the player makes a new character or sits on his heels waiting for the 20% of the time that he's going to get vs. the rest of the time that the others get. The idea that every pc
must be allowed to join the party simply because he is a pc is a terrible fallacy.)
But staying in character, to me, and preserving the roleplaying intensity of the game, is not something that is more sacrosanct than the enjoyment of the game itself.
Do you at least recognize that player 1 might have his fun spoiled by having player 2 tell him that his pc's motivations need to be re-written?
In the original situation being discussed, I think player 1 has a much more legitimate case for being upset than player 2 does. Again, each table is different, but my table includes 'adult themes' and the like. Heck, in a discussion after Book of Vile Darkness came out, my campaign was adjudged to be "vile" in its content- because it includes "vile" elements (human sacrifice, cannibalism, etc), not because those things happen all the time or constantly to or by pcs. If a player is uncomfortable with those elements- which indeed MAY come to affect a pc directly- he has no more place at a table like mine than a player who objected to non-Christian religious portrayals would (or worse, one who objected to parodies of Christianity or elements thereof, which occur aplenty in my game as well).
I guess I fall firmly on the "Game is more important than any one player" side of things- or perhaps a more accurate way of putting this is "Each player should find the right table for him or her comfort zone, but should NOT try to change an established table's social contract to suit themselves."