Eremephobia, is the specific phobia of isolation; a morbid fear of being egotistical, or a dread of being alone or isolated. Sufferers need not be physically alone, but just to believe that they are ignored or unloved.
Harry is a good example of this:
First year, everyone surrounded him, bolstering him mostly for his fame. He disregarded their motives, happy to have people who cared about him, finding close friends in Ron and Hermione.
Second year, it got worse, he found spats where he felt alone, bullied by the school for being "The Heir of Slytherin" However, Ron and Hermione stuck with him through it, up until he killed the basilisk and beat Tom Riddle, once more becoming the hero of the school
Third year, he wasn't alone, the only people who were even rude to him, were Draco and his cronies. His friends stuck with him as he met Sirius in the shrieking shack, and rescued him from the Dementor's Kiss, after learning the true story.
Fourth year, was when it all took a turn. Ron was distant, largely due to what Hermione proclaimed his jealousy, however she sided more with him, for reasons unknown. Dumbledore was forced to leave him alone due to the tournament rules, although Harry didn't know. Sirius hadn't responded to his letters since the summer months, and the rest of the school was still ridiculing him for his entrance into the tournament.
So Harry was sitting by the lake, hiding behind a large rock, curled up in a ball. Stray and errant tears dripped from his eyes as he hugged his knees to his chest.
This was the scene that Fleur walked up on, backstory unkown, armed with only a sudden sense of duty and a need to help.