Spencer tells him that lately she’s been making mistakes and with A back they cannot have her drinking in the middle of the day and be a loose cannon.
In "A Person of Interest," she and Caleb are now in a secret relationship.
In "Someone to Watch Over Me," Hanna finds an owl-shaped pendant in Caleb's backpack and believes it is a gift for her.
Hanna's mother catches them, and drops Caleb's bag in front of them. Hanna decides to leave with him, following him out and camping out with him for the night.
While in their tent in the woods, Hanna and Caleb make out, which later gets more intimate and turns into sex.
For most of the series they aren't that close; only acquainted because of the fact that he's Hanna's boyfriend and they helped each other on cracking A's codes.
However, in Season 3, especially in "Stolen Kisses", their relationship grew and they became friends.Aria and Emily overhear Caleb talking to someone on the phone, most likely a girl, and tell Hanna that he might be cheating on her.