OMGYAY! You picked Rosmerta and Bill (YAYYY), and had lots of other pairings as well! Fabulous :D.
Now, mystery-gifter, in case you were worried that it took me so long to reply to this - it seems as though there's a rule in the universe that fest gifts for me will almost invariably be posted on a day when I have no access to Insanejournal. I swear, it's like some kind of conspiracy of fate and deities and other non existent things. It's happened so many times! But it does always give me a lovely surprise in the evening when I get home :).
I adore that you made Bill virginal, sweet, and head-over-heels crushing madly on Rosmerta. The Rosmerta/Arthur was a lovely touch, too, and Fabian! The saucy lass :). Good stuff.
The ending is win, it really is. Poor heartbroken baby Bill, and then her reaction to Ron... I love that the last line can be read with different tones. It could be wry, melancholy, or a mixture... I do enjoy a bit of emotional ambiguity.
I also (despite being a perv) really like that you kept the sex very PG, because it suited the tone of the story so well to avoid the squishy details :).