It does hurt so bad - I remember a letter that I wrote to my RAH when he was in active addiction and I was telling (trying to tell) him goodbye. I told him that I could feel him in each breath that I took and each beat of my heart. It was a visceral pain that I had never experienced in my life. The ache probably came from my caring for him and my hopes and dreams for my future.
There is absolutely NOTHING that you did to contribute to his relapse. Addiction is a progressive disease. Although I have been sober for two years I can still feel the progression of the disease in me - if I went back out I would be much worse than I have ever been before. By the time that an addict is in the position of your BF it is very doubtful that he is doing anything that considers another person. It's only about the drugs and how to keep it going. Although it's counterintuitive, the only thing that you can ever do to help him is to focus only on yourself and what you need to do to become emotionally, physically, and spiritually healthy. When you go to the Naranon meeting make sure that you get all of the phamphlets that they have - they really helped me. I finally realized that everything that I was doing that I thought was helping was the complete opposite of anything that had the potential to work.
You have started on this journey - simply by asking the question. You will heal and more will be revealed. What can you do each moment to take care of yourself? That is always a good question.
Thoughts going out to you