I'm so sorry to hear that - you sound a lot like me with the sharp tongue and the smarter questions that get us all the information we want and more.
I just want to say your instinct to not ask for more information is probably a good one. My first marriage ended because of cheating in our first time poly attempt, and when he came clean I ferreted out every detail I could think of. I don't think it made a difference to how it turned out since breaking our safe sex agreement was a dealbreaker. All the other stuff just gave me more sad/angry things to think about, and occasionally flip him shit over 8 years later.
Since you don't plan to separate and want to give her a safe place emotionally, it seems like a good start. I see you say you have a therapist, I don't recall if you say she goes to therapy too? It helped my ex a lot to work through the reasons he acted out, and he's a much happier and mentally healthier guy these days.
Happiness will never come to those who fail to appreciate what they already have.