What seems to pain johnny most in life?

There is the fact that his parents neglect him. I think, however, the most poignent moment is when Johnny talks about dying,

"Johnny: I used to talk about killing myself all the time, man. But I don't wanna die now. It ain't long enough. Sixteen years ain't gonna be long enough. Hell, I wouldn't care so much if there hadn't been so many things I haven't done yet. So many damn things I ain't seen or done. That time when we were in Windrixville was the only time I've ever been away from my neighborhood."