My step-daughter has a heroin addiction, and her situation has been up and down. She has been in rehab before, and has been in a sober living house. She said that she really liked the structure. She did not stay clean on the outside. I've seen things go up and down with her--she looks good when she's clean, and then spirals quickly when she is using. Like others said, the addict is very manipulative and lies all the time. The family & friends usually only know bits and pieces and don't even know how bad it is.
It is completely makes sense that you would be mad at him. He has betrayed your trust. Please don't take it personally. An addict cares about his/her drugs first--everything else is secondary.
I also have an AM, and my RABF is in recovery from pain pills. This website is good because it helps you learn how to repair your life. The people here have been through the same thing as you. You are not alone.
If you haven't looked yet, there is excellent information on the "stickies" at the top of the page. I'd also suggest you read the book Codependent No More. All of this has been a lifesaver for me. You can't control your bf, but you can take charge of your own life.