Pyrophiliac

Matthew put on the TV to get his mind off things. His mother recently died in a fiery car crash. On air was a show about people walking on hot coal. This seemed to offend him. He changed the channel hoping for something more empathizing. He was greeted by a food show host talking about grilled chicken and saying "The burnt ones taste better". Matthew couldn't help but smile and cry slowly.
He always had a love for fire and hot things. When he was younger he'd set things on fire just to see their reactions. He had even lit up an ant arm and laughed heavily when the ants ran around in circles while on fire. If there were symptoms of Pyrophilia, Matthew was showing them.
Matthew almost set his house on fire on several occasions. His dad issued a warrant on him, he wasn't allowed to go near anything flammable. He even nearly burnt his psychiatrist's office. Things were getting bad.
Matthew began walking around the entire city in no coherent pattern. People began disliking Matthew and he noticed.
But then at his school, he met a nice girl, who sparked something in Matthew's heart. He was in love with her. They regularly conversed and shared opinions. Matthew seemed to be getting better. Until she showed her true colors. She embarrassed him in front of the whole school. Called him all sorts of names and insulted his love for fire. They even dumped a bucket of water on him.
If Matthew was ashamed, he didn't show it. Matthew looked at her and smiled. He decided to act upon all those that caused him pain. When he got home he dried his clothes and went online, to the deep web, and ordered a flamethrower and other tools of arson. Had tubs of gasoline that could fill a pool.
Ready he was.
He then proceeded to pour them allover malls and other large gatherings of people.
He burnt everyone alive.
Finally he reached school, broke open all doors and burnt everyone down well except for her. Matthew dragged her body to the center of town, ripping open her stomach and forming a pentagram with her entrails as she thrashed around helplessly begging for mercy. He then lit it up revealing a complicated framework of tunnels and pathways he had made that formed a larger pentagram around town that burnt every single thing and person that wasn't already burnt. Matthew looked everywhere and smiled. Their screams of pain seemed to pleasure him. He drank a bucket full of gasoline and uttered his last words - "Being Satan's only son doesn't give me any perks". He proceeded to spark a match and shove it in his mouth, bursting him into flames.