This may be heretical of me, but I'm going to say it anyway:

In situations like the woman described in the Cardinal's book, IT'S NOT ADULTERY! 

Most of us acknowledge this in our hearts, even if we can't quite square it with Catholic theology. We do not treat it as the same thing as a guy skipping out on the wife he is living with. That's clearly adultery. We would not tell such a man - 'continue seeing your lover, but as brother and sister', or 'keep sleeping with your lover but make a spiritual communion". 

Yet we hear those things about the divorced and remarried. That's because, at some level, we recognize that it's not really adultery. It's "irregular", not according to the rules, not the ideal - but not adultery. 

I think our theology of marriage needs to change, perhaps to something closer to what the Orthodox practice. But in the meantime, the guidelines, including the footnotes, in AL make sense to me. Our theology can't figure out every concrete situation.