Mary just can't be the perfect demure angel, and have married John. Just not gonna happen. But that's (another) prequel waiting to happen.

John's going to do his best, but yeah, I think Dean's going to make him work for it a bit. He's pretty damned broken right now, and some of that John might be able to help with. Sam's going to really have to work for it, though.

*grin* Who said it was just a teenaged fling with Andrew? (John may have paid attention, but he's not omniscent.)

There's definitely an explanation coming for Andrew, have no fear.