Sigh.
For those who
truly are still baffled by "that" (like most video hosts and/or cornball critics), the answer is that "that" is redefined in every verse set. He says he'll do a) for love and he'll do b) for love, but then the last line of every verse is the thing he won't do. He won't lie. He won't cheat. He won't whatever. So there are about half a dozen different "thats" over the course of the song, and no big mystery if you listen closely. (I think the first set is a) I'd run to hell and back for love; b) I'd never lie to you for love; c) but I won't forget how you feel like right now (I won't do
that). Clever eh?
Of course entirely too complex for the "She Got a Big Ole Butt" crowd, but whatcha going to do?