My goodness...this is strange. Today, I read the book of Hosea and again I was struck at how much the OT is all about the love of God, the intense love He has for us. I don't think we can even begin to guess at how huge it is. As soon as I opened your thread and read the story, I thought back to that....and then you mentioned Hosea yourself.
If I were to answer the original question you posed as the subject name for this thread, I would say wholeheartedly, 'YES'...God can and I believe, desires to do the unthinkable in each of our lives. I say this from the point of view of someone who's walking a slightly similiar path of betrayal and the agony of heartache. But no matter where I look, all through scripture, is this God who wants to restore, redeem, heal and put back together the most broken of people, the most broken of relationships.
But the key factor to all of this, is willingness. If both partners are willing to literally throw their lives in the air and say, 'Whatever you want Lord...by the world's standards, this makes NO sense...but I'm willing to go where you lead me', then wow, oh wow, what miracles you can see. The number of guys your wife has been with, is utterly irrelevant, if her heart desires to change.
But in your case, then it seems the desire to change isn't there - then if that is the case, truly, then you have made the right choice. I think God guides us in ways we cannot see...He just gently nudges us toward the *right* decision for us. In your case, it sounds like you have moved toward ending it. In my case...I just got a very clear signal that I needed to 'hold on, to be patient...'. The world says it's utterly hopeless, but I believe in a God who is bigger than that. That is also, incidentally, one of the themes of Hosea which jumped out at me today - that God was judging the people because of the fact they were turning to earthly wisdom for their answers.
God's will is written in your heart and, if after study and prayer you believe you have made the right decision, then you most definitely have. And that can only mean one thing - that God has something great in store for you. Hard to believe, when it feels like there is no point in going on...but I have experienced He IS faithful. He is, He is, He is.