The way you are feeling is totally understandable. A few weeks or months of improvement don't make up for years of chaos and dysfunction. It's good that he is trying, but you can't just flip a switch and forget the past. Unfortunately, some marriages don't survive this issue. I hope you continue with al-anon and just allow yourself some time to absorb everything that is happening. I also hope that your husband isn't expecting your to just forgive and forget the past, either. Hopefully he knows it's going to take you some time too.
Don't be so hard on yourself. What you are feeling is perfectly normal under the circumstances.