"Am I to blame for this? Even partially? Anyone, please offer me some hint of an explanation. I need something. Help me understand this! What could I have done wrong? Be a nice guy? Maybe nice guys do finish last? "

No, no no no, you're not to blame. From what you say about your relationship before the affair then there was nothing you could've done. Please dont blame yourself for other people's actions, esp in a situation like this one. It was her choice. Same with the trust - you love her, of course you trusted her. Its again not foolish, it just shows that you are a good person.

Has your wife made sounds to want to sort this all out? If so, how do you feel like that? You're quite rightly hurting at the moment, but please dont make any decisions out of anger, just follow your head and heart for the future. I wish you all the positive vibes in the world in this difficult time.