Makes the Heart Grow Fonder - Fateful Past Connection

Dramas in which the leads met as children or many years before the start of the drama. Meeting each other in the past was pivotal to their lives. 

1 - leads had a single fateful encounter/experience together in the past that changed them but were separated due to circumstance; they reconnect throughout the course of the drama
    1a - one lead recognizes or seeks out the other but keeps their past a secret (* for ML, + for FL recognizes first)
    1b - neither one recognizes/remembers the other right away

2 - leads were childhood friends/sweethearts or knew each other for a longer time in the past, but were separated and don't meet again until the start of the drama
   2a - one lead recognizes or seeks out the other, may or may not keep their past a secret (* for ML, + for FL recognizes first)
   2b - leads don't recognize each other when they meet again

3 - leads had an antagonistic meeting/relationship in their past/childhood and are enemies when they reunite
    3a - one lead recognizes or seeks out the other and keeps their past a secret in order to take revenge (* for ML, + for FL recognizes first)
    3b - leads don't recognize each other right away and become enemies only once they figure out the past

4 - leads were lovers in the past, but were separated and don't meet again until the start of the drama
   4a - one lead seeks out the other but keeps their past a secret (* for ML, + for FL recognizes first)
   4b - leads don't recognize each other when they meet again

Beware of SPOILERS in some of the descriptions