Why Amy?
A few reasons...Mainly, there has seemed to be a little...ummm...frission between Amy and Santos during their conversations. He hired her twice (without even talking to Josh about it)and the job offer in Requiem always seemed kinda flirty to me. Also, she likes power and being close to it...how long does anyone really think she's gonna be satisfied with the lumberjack?(sorry...wood sculptor)...I can see Josh feeling let down and protective of her at the same time... Can see Donna wanting to believe bad things about her, but still unwilling to believe on that scale...and it certainly explains some of the canonical bad blood between she and Mrs. Santos. Also, if Santos is rebelling against the "being in the white house will spoil our family life" constant refrain from his wife, it fits that he goes to the arms of someone who would *never* think such a thing.
Just my take on it...as long as you keep writing so beautifully, I'll be along for whatever ride you throw out there!