Love stories that involve a sacrifice of some sort don't sound as though they can have a happy ending. Well, if the hero or heroine dies to save their partner, that's definitely not happy. No wonder I've never watched Titanic. No wonder I sobbed at that vampire film set in Alaska where the guy sits in the sun at the end, despite the fact that I spent most of the film petrified, viewing from behind the couch. Giving up the love of your life - as in The End of the Affair, or The Bridges of Madison County - yep, too sad for me.
BUT - I don't mind exploring the theme of sacrifice in my stories so long as it never happens. In other words, the H or h are prepared to give up their love, or die for their love. To me that's a much better compromise. Avoids too many tears and we still get the happy ever after.
I used to quite like books that had an unhappy ending. Now, I can't stand to read them. I wonder if it's because life is suddenly seeming shorter!
So, no unhappy endings in any of my stories. That's a promise.