In football terms, Shepard threw Ashley his heart, she then started running with it and then unintentionally fumbled it, she then paced around the fallen heart wondering how, if, and when to pick it up again, and while doing so, Jack came along and recovered... Am I doing this right?
Ooh, ooh, I get it, when she first fumbled it, it was because a enemy player (a collector) tripped her, she fell (was heartbroken), and when she managed to get back up, then she kicked it away, realized what she did, freaked out and tried to get it back, but by then Jack recovered it. Seeing that, Ashley threw a flag in an attempt to bench Jack.
I write on Fanfiction, where Roku, the Avatar before Aang, ascended to somewhat godhood. He's the Aspect of Fire, and hauls the protagonist's dead ass from our dimension to that of Mass Effect. (Sounds insanely cheesy, I know. Still, I can boast with it being more daring, more insane and longer than any other SI's to date.)
Good thing I never played Fable then But you'd be surprised at how well it can blend really. Simple as taking the Avatar timeline and pushing it forward to the same point where Humanity's at in Mass Effect and BAM, cross done right.
You are, however, right in the fact that the crossing easily fucks itself over.