Where are all the good men? I think a lot of the ones I know are in marriages like yours.
OP - your mind is frazzled by love chemicals and hormones that are affecting your body in a way last experienced as a teenager. This phenomenon doesn't just affect middle aged men. Grown women are reduced to silly adolescent girls by the attention and interest of someone they are very attracted to. But you know nothing about this woman. Certainly not enough to blow up your life.
I'm sorry to tell you that this is the easy bit. It's all feelings and fantasy, fog and denial. And I suspect you know how entitled and selfish you are being.
Next comes the justification for the lies and gaslighting and abuse/neglect toward your partner and family.
Then reality starts to seep in, around about the time the intensity wears off and you start to find fault in your perfect affair partner. You'll brush over these things and continue to future fake, but one of you will be lying - mixing fantasy of being together with intusive thoughts of real life consequences.
And then you'll get careless and get discovered -and the lives of the people you love most will never be the same again.
Like any addiction, it gives you a taste of heaven, before it drags you into hell. And to get your fix you will lie and steal and sacrifice your family, your home, your self worth. And in five out of ten cases it means the end of your marriage. I about nine times out of ten, there is no future relationship with your AP, just devastation.
But you think you'll be OK, you can handle it, you won't get caught. Right? But that is how every addiction starts.