I think that there are good things in your situation--although I wouldn't expect you to agree! First off, your wife informed you of her affair of her own free will; evidently, you hadn't even suspected anything. She must not have been comfortable with what she was doing. To freely confess: not many do, I think.
Therefore, she's an honest person and a good person--and apparently a very stubborn person! I think that you must be careful not to appear to pressure her--to push, beg, or to use obvious manipulation.
Another good thing about your situation is your own honesty in taking responsibility for the role you may have played in undermining the marriage. You're quite blunt about it, really.
What puzzles me is why things took a turn for the worse after a period of improvement. Do you have any ideas about this? Did you notice your W's anger at the time of the affair?
I guess that your main job right now is to keep proving to your wife that you have changed, and that your changes are neither too little or too late. You prove that by your actions. Be prepared for this to take a long time. Be patient.
Best wishes!!
I think that others will soon chime in with advice and encouragement. Many people who were once where you are are making good progress--but slowly. Just remember that this takes time.
