Give yourself the right to feel your emotions. You've only been separated since November and he began going to treatment a MONTH ago. That's a very short period of time. OF COURSE you're pissed, and rightly so.
IMO, *live the anger*. Workout, kickbox, vocalize, get some pillows and go to town...write down all the little things that tick you off. In my culture, it isn't justified for women to display or feel anger, which is why I held mine in for so long, but once I allowed myself to vocalize the anger, hurt and frustration I'd felt in the 6 year I was married to XAH, I felt so.much.better. Then I was able to move on to other stages in the grieving process.