This OW is like an addiction. I link it to like a drug addict. H will try to break it off, then go back and forth a few times, hopefully each time (of leaving, resenting) is shorter. Eventually, hopefully the H will come back for good. I have given up trying to put logic into this thing. I just keep reading to understand the pattern that they are going through and try to brace myself when h withdraws.
My H tells me that our M is stronger now. I have changed to put him at the top priority. He likes it when he was (or still is?) in MLC. But now he is in the phase of resenting me again. Things that he likes when he was (or still is?) like me taking care of my appearance (nothing too much, just better from my very very casual self before), getting too thin, etc. But at least he is paying attention to what I am now, which is much better than before when he does not remember anything!!!
I think it is scary for them. They want their old M back, yet you have changed and the whole dynamics has changed. Now they don't know what it will be like going forward. And this time, they (hopefully) are thinking this M, if it survives, will be long term. But they don't know if your change is permanent, or if you will go back to your normal self (that's what my H wants now for me), or what. It is scary. Meanwhile, we have grown so much stronger that we know we will weather any thing that comes our way from now on.
LO, just enjoy the nice H now, and brace yourself when he backslides. I used to tell myself just to treat H as a "date that is pursuing me" and enjoy the nice treatment, with no expectations.