Is a book labelled "romance" expected to a have a happy ending?
I've heard advice that "romance" novels are meant to satisfy, well, a desire for romance, and so an ending without a "happily ever after" disqualifies a book from the genre. And indeed, it's hard for me to recall a "straight" romance that doesn't end well.
On the other hand, romance is a rich genre with lots of character attention; I could see a well-written "unhappy" ending being tragic, but satisfying. And I've just read several YA books (Every Day by David Levithan and The Fault In Our Stars by John Green) which are almost entirely about one romantic relationship, but have sad endings. (Is it possible these aren't romances? If not romances, what are they?)
Genre boundaries are pretty important for marketing purposes, telling the reader what to expect. That's why it's important for me to understand whether "unhappy ending" falls within the "typical" boundaries of the romance genres, or not.