Giles thought you were dead. Everyone did. While on a mission with Buffy and the others, you got attacked by a vampire while the others were fighting, and once they were done, you were gone. No sign of you. It was hard for everyone, but the most for Giles. He always saw you as some sort of child figure, and he was devastated when he realized he didn't protect you like he should have... He was crying for hours on end, not showing up to school for weeks sometimes. It really hit him hard

It hit him harder, though, when you suddenly knocked on his door. You were pretty injured and explained that you simply got away from the vampires which were holding you for weeks, and that was the truth. He had a hard time grasping what was happening, but he was glad you were alright. So glad, that he was clinging to you, continuously offering you some sort of food or drink and asking if you were sure that you were okay. He acted so much like a worried parent...