You know the old adage "What do you get when you sober up a horse thief? A sober horse thief"....I think you simply cannot attribute his infidelity to his recovery from addiction. Just because he was feeling low about himself does not justify dallying around with not one, but two women.
I understand your deep love for this person, but you cannot dissociate the sober person from the drunk person nor from the unfaithful one. They are all one and the same man. Are you ready and willing to accept him as he is today, completely?
As a woman who's been the cheater, several times over, I can tell you that once I started doing it, it just became easier to keep on doing it. Somehow there was a loophole in my head that made it oh-so-justifyable. I reasoned with myself that I *needed* to cheat, and that I would never be discovered. In the end, it just served to destroy my relationships and bring my self-esteem lower than I ever thought possible. And then, perhaps as a little kick in the ass from HP, 6 years after I made a vow to never be unfaithful again because I just refused to be that despicable woman anymore, I was cheated on and got myself a nice STD with it too.
As much as I understand your pain, I hope to also caution you gently to be careful about relapses, as much in the addiction department as in the infidelity department.
In the meantime, be gentle with yourself and allow yourself to mourn.