Saving money is not a good reason to move back in together. Now, granted you two are having a good time together and there has been intimacy, she obviously wants to explore the possibility of reconciliation BUT keeping a foot out the door because she isnt sure it could work out. BUT again, there isnt ONLY ONE way to heaven and life has taught me to be flexible as long as I dont lose sight of my goal.
The thing is, that IMO the situation could become very nerve wrecking and the fragility of living together without a mutual understand of what you are b oth aiming for, could and will test your sanity. Are you up for that? Are your feelings still strong enough to motivate you to hadnle the sitch?
How about the kids? Dont get me wrong, I am not saying it is a necassarily bad idea, just pointing out, that unless things evolve relatively fast, you should better fasten your seatbelt for the ride...
