I have been guilty many times of making the ultimatum to my recovering A and not following through -- wanting to believe he will come around and taking him back at the slightest sign of remorse...
The fact is that even when they aren't drinking alcoholics have some incredible mechanisms to support their bad habits that are not drinking -- avoiding commitments and responsibility is the main one I have trouble with. My (now ex) boyfriend would do terrible things along the lines of cheating, abandoning the relationship, etc., beg me back, only for me to find out that he has no intention of stopping the behavior and in fact has found a wonderful way to blame me for it! The reversal of blame is pretty amazing. Anything I said was used against me, twisted and distorted, and when I drew the line in the sand he would just hang up on me, give it a few days, and then try again.
It has been so hard for me to stay out of it that I am actually considering jumping right into something else so that I can be done with him once and for all. The latest episode in which he told me that his enabling sister hates me and has told him as much...I told him that he can't defame me with his family while apologizing for his wrongs and promising to change -- that I cannot bare the burden of our problems and the blame anymore. I wanted to have a family and instead what do I have? I don't even have a relationship in which I am respected. I dread and fear the day he contacts me again to try to rope my back in with his flowery recovery language ("I feel a shift in myself", "I've been struggling with this my whole life but today, this week, everything has changed!").
Be warned: recovery is sometimes just a means to acquire more tools to manipulate, use, and ultimately destroy other people. An alcoholic in recovery can be worse than a drinking one if he isn't working on the underlying illness.