Eddie wants to stop living.

Every breath he takes he wants it to be his last. He wants his last day to be a good day, and that seems to have finally happened.

Richie came up to him and asked if he was okay, of course he said yes. Then Henry punched him, but Richie actually talked to him.

His parents weren't home, so he didn't have to deal with them, and his brother left him alone.

It's not as if anyone would care if he died, he has no one, sure if his parents were sober they would mourn, but they would get over it.

He gets ready by sending three texts, one to his parents, one the Henry, and one to Richie.  He tucks his phone away, and gets his bike that's been sitting on his step.
After biking to the quarry he says his final goodbye to the world, and leaves silently, falling into free fall.

His wish came true, he took his last breath.