J.D.
question: why would you invite him back in if you've obviously got that much fear that he'll flake out again?? Why in the heck would you even risk your heart AND YOUR CHILDREN/S hearts until you are S-U-R-E he's going to stay, until you're sure he's determined, changed, dedicated?
if it were me (or if i were giving advice - i THINK i'd do it this way) i would make him 'date me' for at least-at LEAST- 6 to 12 mos. that would give you more assurance and should prove to you that he's got the discipline and responsibility to actually BE a husband again.
i would probably register that separation paper, to prove to him that he has to walk the straight line. i would suggest you not let him back into the house, keep separate accounts (you take the money!!) you could also go thru the divorce and then remarry if and only if he proves to you (like he did the first time)that he's 100% in for good.