Mila, they are like that at the beginning. It's not you, it's them. It's not that he doesn't care, it's that he's not thinking like he usually does. It will pass.
Also, what CW said is true, about the rope. Right now he has nothing to lose, so why not do what he's doing? He's not loosing you, you are right there. But it takes time to see and you are still so early in this. I'm at almost a year, and dropped the rope somewhat, and H is finally really starting to see what he might loose. It's just the way it seems to work, who knows why.
And OW complicates things because there's a hormonal high that he's influenced by and there is nothing you can do about that. It will wear off, but not today or tomorrow. It will take many months to dissipate.
It would, however, be helped by OW loosing something as well. What is wrong with OW's husband? Why is he letting her into the house all the time to be with the kids. Does he think she will be seduced back to her family by chores? She has to realize what she will loose too. She left her house, so technically she abandoned her kids. Nice. He will probably get tougher eventually, and when that happens, with both of them standing to loose too much, new doors will open up.
Until then, stay strong. Try to remember that time must pass for things to change. I know it's impossible and the feelings are rotten, am there too . Breath deeply. Take one day at a time. Just tell yourself that you are not going to react... today.