So they know each other from long time but suha doesn't remember him or what

They know each other because president Lee take in Suha's family since Suha is in highschool (I guess because Suha once said he and D.Park met when Suha is in highschool and D.Park is in junior high) there's another reason on why they're close is because Suha's sis talk very familiar with D.Park.... anyway their family relationship is still confusing because of their surnames.