I'm sorry you feel hurt.
It's not fun to hear of past indiscretions when you are trying to build something there with him. Makes his word TODAY hard to believe in when crazy from the past pops up.
How can you KNOW he doesn't lie to you? How do you know he's willing to be held accountable to promises he makes you? Of course you are thrown for a loop! It is understandable to feel upset.
Right now he behaves like this...
Now he is evasive and slinging shots that I should understand and how he never questioned any of my former relationships.
Could that mean he expects you to be ok with him lying and keeping things from his wife? What does he keep from you?
You are the one in relationship with him. You could decide if this is something you want to keep dealing in or not.