I had this similar thing happen before, more then once. Every time, later I discovered that he indeed was using again. That I went on this emotional roller coaster feeling guilty, sorry for everything and I was again being lied to and manipulated. This "I'll always feel like a failure to your family" is an invite for pity (sorry if harsh, but addicts always seem to want forgiveness right now, instantly)
Just don't put it past you.