Go slow. It is wonderful to hear of all the changes that your husband has made. But let’s review the process. You have been separated for a year and a half and it came about because there weren’t significant sustainable changes. Now that you have started dating, your husband has been highly motivated. The question really is whether he is motivated for you or for him? Only time can answer this question. It is for too early to think about reconciliation, although a couple months is a very very good start. But that’s all it is.
It doesn’t sound like you have any big decision that needs to be forced. I would be sure to tell your new boyfriend about the struggle and don’t try to hide anything from your ex. In other words, get on with your life and see what evolves. If you see sustainable changes after a year or so with your husband, it may be something to reconsider. But before that amount of time has gone by I wouldn’t use a couple of months as the best indicator that the change will be long-lasting and something he’s doing for himself.
As you sort through this I would highly recommend individual therapy. The find help tab at the top of the page should help you find a local therapist in your area. You’ve taken a long time to make the decision to leave. Give yourself the opportunity to view this process with your husband from a distance. You don’t want to jump back in too soon.