Sending you a hug. I realized XAH relapsed after my son's cough syrup disappeared (mind you, XAH was the one who obtained said cough syrup from pediatrician, when DS had pneumonia and did not even need it). Once I thought of it - he was "off" right after rehab, weird behaviour, not looking for a job right away, not eating. I cannot describe the feeling, but I asked him not to come back (he was staying with the friend after rehab). He was in two rehabs back to back (eloped from the first one), I paid serious money down for each one, and here he was, two weeks later, chugging down DSs medicine because it had codeine in it.
Be strong - and don't tie your self worth to his being sober or not. Nothing you can do about it - time to detach.