Where they "meet" by exchanging letters (such as thru a newspaper ad) and they get along wonderfully.... and then they arrange to meet in person....
One has to court the other, in traditional wizarding ways. Either because they are infatuated with teh other, or because albus insists on it to prevent some alternative (like lucius claiming harry etc)
Courting again, but where it is done in secret and the recipient is puzzling over who is sending them all these gifts / love letters etc
THey get locked in a room and cannot get out until they get over their differences and have sex