For me, I think that as long as H is in a relationship with OW, there's no point in me really worrying about him coming back or not. Right how he's in a "fog", and the part of his brain that thinks rationally is turned off.
I've decided that while he is of the mind he wants to end our marriage to pursue this other person (who lives 2500 miles away!), he is my business partner. He is not my friend, and I do not treat him as such. I communicate by email around things pertinent to our "business" (our S7), and the dividing of assets (he's rented a house a few blocks away).
When he is here to drop off/pick up S7, I am pleasant and cordial, but I don't engage in idle chit-chat. When he is here packing his things (a process I hope will be over next weekend), I remain pleasant and cordial, much like you would with someone who struck up a conversation with you in the grocery line. Again, though, once his business is done, I don't let him linger.
This helps me, because I need to not interact with him, for my own emotional help. It also allows him to see my pleasant side, without the benefit of any long-term exposure to my company or the emotional need it filled.
My theory (and this is a common one across these boards) is that by going "dim" (not totally 'dark', although will be darker once he's completely out), it allows him to look to OW for *all* his emotional needs. If/when she is unable to meet those needs, he may eventually realise that and start behaving differently.
If not, I'm still doing what's right for me, for my emotional health.
H: 39, Me: 37 SD: 18, S: 7 M: 9, T: 10 "I love you but am not in love with you" - 5/11 Discovered online affair - 7/11