Ginger is right, I have a friend who recorded conversations between his wife and OM mocking him for roughly the same things you are doing.
I know this $hit is hard as h3ll because you feel like your entire world is crumbling around you.
You think that being supportive and nice is the right think to do, especially if you feel your actions in the marriage pushed her into the affair.
You think that if you show her how much you love her that you will always be there for her that she will come to her senses and say "WTF was I thinking"? Unfortunately, that BS only works in today's movies.
Do you think Clint Eastwood, James Bond or James Dean would say something like that while their wife's were in extremely open affairs?
I understand your point of not wanting to close any doors and being the lighthouse but you can do that while also being firm and communicating that you will not be treated this way.
I will end this with a story in which my best friend who wasn't married but lived with the mother of his two kids had an affair with a woman at work. The woman at work D her husband and dated my friend for 3 years. The minute her ex-husband started to move on with his life and starting dating another woman, my bf's girlfriend left him and went back and remarried her H and they are still married 10 years later.