I would be very wary for the next 6 months at least, that is if he lasts that long.
I guess if my bloke told me a lie about the day he was coming out of rehab, I would be interested in finding out where he was for that day and night. Sharing him with his recovery work is one thing, sharing him with some other chick, no way and goodbye.
You are his wife, and you have a right to know.
Personally, if he is so into this woman, that she knows his every move better than you do, why not let her "support" him thru recovery.
Sorry love, something pongs in his behavior.
God bless