Before I begin, I just realised that the name campman comes from him being the camp man. Get it?
Also, when he asked if I thought he was crazy and I said yes, his responses were different from my previous playthrough when I said no. He claimed I fed Clementine human meat (Mark's legs) even though on my save file it never happened (I copied my first save file to my last two with only the last two episodes different from the rest.) Yet Lee acknowledged it as if it was the truth. I don't know why, maybe Telltale didn't think that through.
Now to begin, if you tell him that you hurt someone by responding with a yes, he will ask who. Say the wife. He will then ask how. Say I did a lot of things. Then it will reveal Lee's backstory. Apparently he always wanted kids. His wife was always working and she got mad when Lee wanted to settle down with her. Apparently they were never the same again. When he had a sick day off from teaching school, he goes home to see her with that man.
So, that's it. Apparently that guy Lee cut his guts open with the knife is Ben. Doesn't seem far off from the truth.