Publicly, Merrin is upset with Fast-Hands because he has failed to show proper respect to the goddess and the spirits. Secretly, they had an affair that ended badly, and her feelings are hurt. She'd like him to apologize, and maybe even to continue their affair. He's not so sure about getting back together, but can be cajoled into apologizing (you can even talk him into making an offering/apology to the spirits in front of Merrin, when she's the real target, which keeps their affair secret. That will fix the situation and she'll fix his leg if it hasn't already been fixed yet.)
Combat Boy - Can beat him up until he agrees to apologize. He could beat her up, too, but that would be stupid.
Science Boy - Can bribe her with tribal medicines or the dog-allergy-relief stuff mentioned in the Marie's apprentice quest.
DiploBoy - Will have the best chance of convincing them to make up, either through intimidation or diplomacy.
Stealth Boy - Can sneak around their homes and find some clues about their secret affair, confronting them on it and making them admit (to the PC) what the fuss is really all about, making the speech checks easier (and allowing you to take the ChaBoy route with lower skill totals on your end).