Analysis / Bittersweet Ending

• A common reason for the Bittersweet Ending is to be fairly realistic: Not everything you do is going to end the way you want, but you can still have some of the other positive benefits or even gain something you never thought you needed/wanted but wind up with and end up treasuring.
• Following from the above point, this type of ending can offer some valuable life lessons:
  • The Official Couple break up for good and while both are saddened by this, they handle said break up mutually and respectfully, both acknowledging their own faults in said relationship. Years later, while they don't communicate with each other and have fully moved on in their lives (possibly with new lovers), they each hold a special place in each other's heart. The lesson? Break ups can be hard but sometimes it's the best option when the romance isn't working.
  • The Hero Dies defeating/killing the Big Bad but the world has been saved, his friends/family can have happy lives, and their main Love Interest is carrying their child. The lessons? While it's fantastical in nature, it shows that sometimes to achieve the greater good, sacrifices may need to happen, including the heroes'.
• It's a combination of the Downer Ending, Happily Ever After, and Earn Your Happy Ending tropes all at the same time: You're going to be sad about some events but still gain/keep something that truly matters, and sometimes the sweet part is worth all the trials and tribulations you went through.