Since you asked... Yes I graduated from BBS, yes I am a Christian, and I am very familiar with the story of Jesus' encounter with the woman and her accusers. Very familiar with forgiveness...been given a whole lot more than I ever deserved, and I do my best to give it as well.
In spite of your cherry-picking from the Bible, I will say that in addition to forgiveness, we are taught that sometimes there has to be justice, personal responsibility, consequence even when there's forgiveness, and that "the devil made me do it" is not an excuse from my own accountability.
My question of your repeated attempts to excuse and justify your buddy was not "un-Christian".