The only advice I can offer you is to try to keep a positive attitude and continue to do the things that initially attracted your H. Although there is no set timeline, I read somewhere (maybe Starsky?) that those feelings can take years to fully return.
True, but only if OW is completely out of his life, which obviously has never happened. I think the daily contact with her at his office may have blocked him emotionally to mdu's positive changes, and caused him -- a waffler already, imho -- to waffle even more.
Wars are won by FIRST pacifying your enemy. THEN you negotiate the peace. I don't believe it can be done backwards. (I know that sounds harsh, but when a spouse is wayward or walkaway they are an enemy to your marriage and your intact family).
I don't think the man was ever allowed to hit bottom. Maybe he will if mdu moves on.