If you want to encourage role-playing, why not aim for a character/romance who is multi-dimensional enough to not drop someone for one misstep. A man or woman who can forgive? Who can see that a person might be worth enough to say "I didn't like that, but a long term relationship with you may still be worth while, please don't say that again". Who, well, actually communicates?
We play these characters who fight dragons, the undead, evil mages, through all sorts of obstacles and hardship, but seem to have egos made of eggshells. It always bothered me with the Bioware NPC romances; I had hoped for more resilient NPC romances from mods.
A romance would be particularly interesting if it had multiple endings (other than 'good', 'bad', and 'indifferent'). Where the NPC can be pushed a little, and pushes back. Who is sometimes not on their best behavior, and realizes it; or needs a good dressing down to bring them back to reality. Who needs to sometimes be forgiven, but can also forgive.
I'd love to write a character like this, but I know next to nothing about creating BG2 mods.