I have a very skewed idea of "Happy," especially when it comes to romance. Almost all of my books feature vampires. And usually, only one party is a vampire and the other is a human. To get their happily forever after...well the mortal has to die. Sure they come back, but this almost always leads to abandoning everything they have ever known in favor of being with their vampire lover.
To me that is happy. But I can see how some people might disagree. For the most part the vampire turning is implied. With the exception of one book the reader doesn't see the "dirty details" involved in a "forever after." It's more pleasant to think of the good and let the bad fall to the side.
Sure, at the end of every book the hero and heroine are together and happy and in love. But can a reader forget everything that has taken place before? All of the hurt, the loss, the pain that I have thrown at them as hurdles to get together in the end? Can they forget what the hero/heroine is going to have to give up in the future to be with this one person?
I don't know. It seems to be working out, people are still reading my books and seem to like them very much. But I am a cynic. "Committed couple at the end" I can live by that code. I just don't always know how happy that really is for some of my characters.