I think the overriding theme of this story would have to be the "maturing" of both Robbie and Brad, where they finally learn to put the idiotic things they used to do in the past and act like men, not adolescents. At least that's the concept.
Another thing that's been fun to do with these stories is to portray the Hayes family in various situations, and observe their outcomes. Jeff was bright and talented but doomed to fail, yet he came from a hellish home. Matt and Gathan are both successful, and they came from stable homes. I'm not sure I was planning this to be a dissertation on environment and its impact on kids, but it seems I'm ending up there anyway.
JP is a very thorough person, and usually is on top of things (well, not all the time ). He's adept at anticipating problems and outcomes, and then planning to forestall disaster. He's pretty much done that all his life, especially with the men he's been with, all of them except Jeff (and Sam). For an achievement oriented person, I can see where Jeff would haunt him, because he would think that he failed with Jeff. Further, his state of mind in 1968 was so uncharacteristic, what with being in the midst of revolutions and riots, job changes and moves, etc., that he probably wasn't thinking things through as clearly as he otherwise would have. He'll note that, and take that burden on himself, and that's the fire that fuels his guilt. Could he have done more? That's the sentence that haunts him.