Used between couples in a relationship to address each other. Normally used by younger couples (old generation does not use this phrase), and can be between unmarried or married couples.
It can be addressed to both men and women.
In Korea, the wordliterally means "Self" - so you are literally calling the other person as yourself. So that implies the other person is your self, your other half, your soulmate, you...
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.
A lighthearted reaction upon receiving disappointing news of some sort. Usually something that isn't a particularly a big deal, esp. when it primarily affects someone else - sort of a mild schadenfreude. Sometimes doubled or tripled, and possibly said in a sing-songy voice for added comedic effect to imitate a muted trumpet, which is how the meme originated.