Well, all I can tell you is that once the R supposedly shifts from a WAS/LBS situation to reconciliation, the rules change somewhat and I think there needs to be more openness (yea, I'll try to take my own advice here too, lol) and you should be able to ask these kinds of questions. What's the worst that happens? He thinks about it decides that he doesn't know why he's back and thus should leave again?
My point is that I too don't know if you should do it today, or ever tomorrow, but at some point, I think it's entirely appropriate for him to answer WHY he's back.
My W just kinda did that when she "came back" so I didn't really have to ask, but I know if she didn't do that (and really, even though she did, I STILL want to ask more about it) I would feel a strong urge to ask her.
I would say just give him a bit of time. He may come out with it on his own. Then, if you still need to know and too much time is passing, ask him.
