I'm recognizing that he seems to respond much more positively to my being in his presence and actively doing things with him. I'm sure it's completely cake-eating at this point. But for the remaining time I have left here, I am going to put my best foot forward to be the best, most attractive person I can be for myself.
AFG,
I think so long as you're doing it for YOU, you're fine. If you start doing it for HIM, to get a reaction, and your expectations start going up, that's a red flag for you.
The other red flag would be if it feels AUTHENTIC to you. If you can honestly say "This is the kind of person I am, whether or not he appreciates it" (a good example might be saying "please" and "thank you," or giving a sincere compliment). If, however, it makes you feel LOW, like a doormat, then you should stop.
The problem you're going to have is, so long as he is getting some of his physical and emotional needs met by OW, and some of his other emotional needs met by you, he will continue to cake-eat and never make a decision, until the situation is acted upon by some outside force. Now, it may be that the "outside force" is OW dumping his sorry azz, or some religious epiphany on your husband's part, but outside of those two things, I think your approach is going to prolong his waffling, I really do.