I have no way to relate to what you wrote. You have my deep sympathies and condolences. I have one son, now 28, off exploring S.E. Asia and I can't imagine how I would handle him dying. I too regret the times missed, the arguments we had, misunderstandings not corrected... but at least we do get to do things together.
I will say that I have immense respect for what you wrote above. I know I wouldn't be able to do so. At least I don't think so. So with that, you seem to be at least one step off in the right direction.
It would do no harm at all to find a grief counselor or psychologist. You should not bear guilt. That may be one of the hardest things to shake, but you must.
The "Christian" thing. To me (forgive me) that has the trappings of insulation when you need, over some time, to grieve, to cherish memories, perhaps write those down as part memorial and part therapy. Raw. Don't let anything be between you, your son and your feelings.
You should also consider your wife's grief as part and parcel with your own while bearing in mind that you will both go through this differently in terms of expression, listening/hearing/interpreting, time ...
Again, I'm very sorry for your loss and I do hope you come through with this tragedy lighter on your shoulders. In time.