Sunoo is a very bubbly person, although when it comes to the topic vampires, he avoids that word every time he hears that. It's hard to keep such a secret hidden from the human world.
He decides to move to a university to control his thirst for blood. He knew he needed to control his hunger and stop looking at everyone like living blood bags.
Then you two met. He recognized you, he felt guilty for being the reason your dearest family member died years ago.