My Pathfinder/D&D games tend to involve relationships – romantic, friendly, etc. – between PCs and NPCs alike. 3.x only has the Diplomacy mechanic for any kind of relationship mechanic. I'm interested in ideas for mechanics to help represent these attachments in the game.
Not as a substitute for roleplaying, but to encourage and represent the relationships. Tracking them, leveraging them, determining how NPCs respond to them.
I've seen mechanics like this in various indie RPGs. For example, the zombie survival horror game "the dead" allows characters to roleplay and build up the strength of their relationships, and this grants bonus dice you can use on checks made to help out the person you have the relationship with.
As a stopgap measure, I tend to use complex Diplomacy checks over time to track overall positive/negative attitudes towards PCs from NPCs. I make sub-checks to determine if romance is part of the equation.
Example: Female NPC paladin meets PC monk. Initial reaction roll: 17. She's quite impressed by him. They have some differences but are both generally Lawful and whatnot and he acts civilly so I don't put any modifiers on it. Next time they meet, the reaction roll is a 20 – I decide that's a "spark" and she's really interested in him now. I make notes with plusses or minuses to indicate particularly good (15+) or bad (5-) reactions. So on the paladin's NPC index card, I put the monk and two plusses by his name to indicate the general impression she has of him. Next time they meet, the reaction roll is a 10, which given the two plusses I interpret as still favorable; she's not going all stalker but likes him. And so on.
What are some rules you use, or ideas for them, to better represent relationships of various sorts? I mainly play Pathfinder but really anything even vaguely d20/D&D compatible would be interesting. Ideally it's a simple way to determine how favorably a NPC sees a PC or other NPC and then ways in which that impacts life.