I know what you mean, when my H first started saying "ILY" or being concerned about me, my brain found it very difficult to believe him. Once night I inadvertantly pulled his wedding ring off when I took my hand out of his while walking, and it rolled almost to the sewer grate. He snatched it up, exclaiming, "Oh no--it would have been dreadful if I lost this," and I just felt this huge disconnect, thinking "but 2 months ago you couldn't decide if you should leave me for the OW and the ring meant nothing to you...." It took a lot more consistency from him before any of it felt real to me.
Yes, he can be falling back with you, and is! You don't need to reply to his ILY's until you really feel it, though.
As for your earlier question, my H told me very little about the things he was working out in his head about the OW, which was probably just as well since it took him months to work through all that. I'd say it's a really positive thing that he self-soothed to the point of being in a good mood by bedtime already--that's healthy behaviour on his part.
