Mars,
Is he just paying visits to the rehab centre or is he doing daily Naranon and AA meetings? If it's the former he sounds just like my ex who only managed a month tops before relapsing to the worst he's ever been.
In my experience they need to work a very strong programme to stay clean/sober especially in the early days. My thoughts are if they can't commit to themselves and their recovery how on earth can they commit to another human being.
I know it's tough to deal with as us codies always want to see the best and believe the promises that this time it will be ok, but sometimes we hurt ourselves as much as they do with our own behaviours. Some times it's good to be a cynic