Come on now, kas….you have to stop doing that to yourself. You are projecting what YOU think is happening onto his life and just dragging yourself down in the process. Stop worrying about it, thinking about it, focus on you and your kids. You have NO idea what he is thinking or what she is thinking so speculating on that is just stealing your own joy. You just mentioned your GAL as sewing and finding a great deal on a machine that should have some sentimental value, but yet you focus on the OW and your STBX. Remember that shiny and new things get dull over time and he is likely on his best behavior right now for her, but the new will wear off and at some point, she will get the same version of him you did. Don't compare where you are with him now to where he is with someone else in the new stages. It is NOT the same place. You have the capacity to really recreate your self and your life here and really have a great experience with your kids. Focus on that and stop worrying/wondering about what he is or isn't doing. In reality, you really don't know if anything you described above was happening or not, so just let it go.
And, yes, I know that is way easier said than done. You asked a few posts back and several responded that it really all does get better. I'm sure it doesn't seem like it in the moment, but everything will get back to normal for you. It will be a new, better normal and you and your kids will be happy. Don't rush it. Take the time to heal, but I can assure you it DOES get better. Time heals all wounds.
Me 52, H53 Bomb drop 9/29/2014 Divorce from XH final 12/17/2014 Marriage #2 12/31/2019 5 adult (step)daughters (3 from XH's first marriage, 2 from current H's previous relationships) 6 grandkids