I think like other posters have said, JH is trying to work things out.
In the past week, I lost a young family member unexpectedly, who wasn't much older than Lucas, to a brief illness. We thought it was getting better, the doctors were positive that it wasn't a fatal condition and would respond well to treatment and he had a long normal life ahead of him, so because I was lucky enough to be in a position to do so, I stopped work to take care of him 24/7, because we all truly believed it was a blip and he just needed to get on the right course of treatment.
I'm sure anyone who's taken care of a sick relative can relate to this, but maybe more so if they're young - you have hope. So in JH's case, even if the child is missing, until that body is found, you have hope. It may be as plain as day that the child is more than likely deceased, but there's this hope that something will make it work out. Somehow.
In the past week where my family member went downhill, there was still hope, thinking back it was probably not as hopeful as we imagined, but the doctors were still none the wiser either - I think that's much like the situation with EG ; they didn't have concrete proof that she murdered him (nor do they yet) so JH would have that hopeful instinct to believe that EG wasn't responsible and it was all a terrible mix up and that maybe Lucas was OK etc.
In my case, my family member went down hill in a matter of hours, for reasons that have baffled even the specialists and even though they tried hard to save him, it was too much for him to survive and we had to make the decision to let him go.
When I was half asleep last night, processing everything that'd happened, my mind was still in the phase of "but we could..." then I remembered that no, it's now over with, he's passed. I think it's a natural inbuilt instinct where even though the circumstances change - a passing or the locating of Lucas, your mind still defaults to the buts, the maybes, the logical processing methods that you use when trying to solve a problem that has no reasonable answer. I think for JH that may be the case, as yes, he has more information, he knows EG placed the body in the culvert so he knows she's the last one to see him, that she held his dead body and that she hid it from him and didn't tell anyone Lucas was out there, but his brain is probably fighting that "But..what if..." motion.
I think a lot of people can relate to this comparison and whilst JH isn't an angel or even been a help to himself in this situation, I think the obvious fact is this is incredibly hard to process and he's not at his best whatsoever, no one thinks a situation will end in your partner having a hand in the death of your child, so he's going to come off as a whilst he works it out - but he's clearly having to process it, fight it and process it again, IMO anyway.
