Just caught up with your sitch, Erin! Hope your foot is feeling better, and S2 is healed from his burns. I remember what it's like to have little ones - very stressful.
My only advice now, is to take care of yourself, emotionally, spiritually and physically. It's good that you run - I started working out during my darkest times, and it really helped me.
What helped me, eventually, is that I finally decided that D was the best option, that I needed to move one without H. It helped me to detach, and I was able to calm down, and focus on other things. I was able to be myself more, and not worry about his moods, or what he was doing. As it turned out, he eventually ended the A by himself, and then pursued me again. I was very surprised, and not sure if I wanted the M by then. A year later, and we are still together. very unexpected!
Anyway, hang in there, go with your gut, don't get discouraged, find a way to know that you will okay with or without him, and you will. Don't ever let him make you feel responsible for his lack of judgment, and don't second guess yourself re your choice of H and father of your child. You did it with the best intentions, a loving heart, and he messed it up. He obviously has unresolved issues that he is, at present, unwilling to deal with. Probably using OW as a band-aid - the excitement of an A can cover a whole lot of stuff, but it won't last forever. The OW, at the moment, doesn't realise he comes with baggage, and once the fantasy, infatuation part of their R is over, it's going to all become quite apparent, I have no doubt.
Stay well.
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim