Canis said:
Any DMs want to share how they build a romance hook to make sure the player takes a good bite?
This worked for me in the past.
Find the player who is most open to a romance. Throw him some little flings and such; try and make them unfulfilling.
When you introduce the romantic interest, either describe her as someone the player thinks is hot, or as vaguely as possible, letting the player fill in the blanks.
Don't make the romantic interest fall for the PC right away. Have them be friends for a while.
Make the NPC competent, a valuable asset for the PC (not the party, that doesn't matter). For example, I gave the PC a bonus to his gambling skill whenever the two of them worked together. You could do this with Bluff, or Diplomacy, or even let them communicate with Innuendo even if they don't have any ranks in the skill.
Slowly develop the NPC. Reveal secrets about her over time. These can lead to adventure! or not.
When it's time (like the night before a big battle), have them fall into each other's arms.
And don't go into details about the relationship. Talk about it in 3rd person; don't speak from the NPC's mouth. Let the player fill in the blanks.
If it works, hopefully the other players will be jealous and try and find their own romance.