I'm sorry but if it was "innocent" then he wouldn't be using so much of his energy to hide things and keep them from you. He wouldn't be blaming you for things. I don't think it's healthy for him to be forming such attachments to women in AA PLUS the fact the he works with her and sees her even more often than he would if he just knew her at AA meetings.
If he really wants things to work in the marriage he should be willing to not form emotional relationships with any other women.