I tried to post earlier - let's see if this one goes through.
What about Midnight in the Garden? You could do fairy lights, flowers and fountains, garlands - very romantical
The social chair manual has a lot of other ideas that may spark some creativity.
Oh, just a reminder that Pi Beta Phi does not allow alcohol related themes. Make sure you have your AAC approve the theme you choose before you begin planning.
PPL,
cherub