Abs - I'm sorry. I'm not of much use right now - but you're getting some great advice here. Keep your boundaries up and I think the rules should be layed down early on. Addicts do lie and it has been part of "him" for a while now depending on how long he's been addicted. I too don't trust my AH farther than I can throw him. I think the best thing that you can do is reiterate your boundary with lying. Don't let the lie bring you to weakness, use your strength and be firm with what you will tolerate. Don't let it send you in a tail spin. I agree with Anvilhead and her firmness. You're in new territory right now. You're both trying to find a new way, but old habits are hard to break. It would be very easy to fall into the same roles of the codie/addict - even without the drugs involved. You're learning a new dance right now when you've done the same one over and over for a long time. Change is hard on BOTH parts.
Of course we don't want to be lied to at all on any level - but our reality has been lies and they probably won't stop cold turkey. But reinforcing your boundaries and being firm in your stance will show him what you will and won't tolerate. If this lie sends you in a tailspin, you're giving HIM control. Take it BACK and put the ownership of the lie back to him. It's HIS problem if he chooses to lie, NOT yours. Make him aware (I'm sure he is) that he's walking a thin line right now. Hugs to you - BTDT - you think after rehab the slate is washed clean - but signs of that old "dance" can send you in a frenzy. It did me I know. I see now that rehab was the war, but their are many battles after the fact.