Getting characters to fall in love

[eloisem.livejournal.com]

I need my main female character to fall in love with my main male character because part of my plot twisting at the end hinges greatly upon it. Only thing is that I can't seem to get them to fall in love with each other. The story is set in a medieval setting (but no magic or anything), so it's not like they can hook up via myspace or whatever. They know each other, they work together, and they flirt a lot - so anyone have any ideas on how to get them to fall madly in love?