"I don't think that there is a specific OW - more a general idea in his head of a sort of sporty, ageless woman that he sees from looking at too much social media. I suspect with an underlying issue with stress at his work and issues with his family he is looking for something to make himself feel better".
With kindness OP i think there will be another woman eventually, if he starts to feel trapped. I felt like yr DH when i came to end of my marriage. Everything he did annoyed me, he was happy to sit at home reading at night, sneeze loudly and yawn, no ambition, buy his clothes from Sainsbury's and suggest i do same! He was really just dowdy and boring. I managed the house and children well and worked, i am very organised. My running of the home and DC's gave him the freedoms to just sit there reading about football! He has a good job but it was everything else that put me off. It happened over yrs. Every facial expression he made turned my stomach. He was a good father but was ultimately holding me back. He was just not very motivated , whereas i am. I had a very successful career and social life before i met him, my own home and money. All those i had , propelled us financially
to where we were. He just stagnated us to be honest once i had children.
Basically , he took the easy/least effort option and it made my stomach turn eventually. Therefore his sneezing, yawning, his pubic hairs left in the shower, his jeans that took days to dry, as he was tall , his lack of need to look good , make an effort, all pee'd me off. I take great care in my presentation , always have, even with young children, i made time for me. He was always told by his friends i was a keeper and he was batting above. He was not house proud either, i am, and he used to leave a trail of crumbs when he ate, like Hansel and Gretel.
In my early forties i just felt i needed more. No affair , nothing. I had had enough and we ( i said it was over ) put wheels in motion to separate. He would have been happy to plod along- he thought all was good. I was unhappy. Everything about him grated on me, i did not fancy him anymore and he was putting limitations on my life just because of who he was and what he wanted from life. Both of us are happier now, co parent very well and i am free to advance myself. My children were/are happier also, as they are more my character.
I think OP , when a partner or spouse starts to complain about your chin, how you look and yr weight, the attraction has gone. When they also feel they do not have as "fuller a life" as others, it is the beginning of the end. Looks to me like your DH has the " ick" and is sowing the very early seeds for the end of the relationship.