He is right, it has nothing to do with you.
My SO is in recovery and it is still a rollercoaster for him emotionally. When he relapsed, it was awful to see him in that state but the more I tried to 'involved' the more he distanced himself from me. All I could do was pray and keep my fingers crossed that he would work himself back to recovery.. and he did.
If your bf was doing great with recovery and relapsed, hopefully he will get back to recovery and learn from it (assuming he is working a program). Oh and do try Al-anon.