While the phrase "Happy Ending" often refers to a generic story trope where "they lived happily ever after", it is also the title of several specific creative works. Depending on what you are looking for, here are the most prominent "Happy Ending" stories:
Widows or divorcees finding companionship later in life. The Happy Ending
Career or financial struggles that eventually resolve into stability. While the phrase "Happy Ending" often refers to