I agree with name.
The thing is, we want the most what we can not have, we lust, and crave something different. WE covet what we see everyday. The reality is, even if you are with her, if you have your fill and leave your wife, quickly you will find yourself bored and missing your wife and what is familiar, we are often attracted to the unknown and in the end, majority of the time in a situation such as this, we end up miserable. You are not alone in this, and so many people have ruined their lives over such a frivolous affair. You need to take a long look at your wife the next time you two are alone. Look at her good and hard. That woman right there, has easily put up with you in some of your worse moments, she gave you the gift and the promise of her love and her body for the rest of her life, she isn't young anymore, she can't just start over, this is no longer the spring of her life and she has settled her heart on you, and you should consider yourself lucky to have someone who gave that to you, 40 years of precious time they will never get back. Take it all in friend because those worn hands, those wrinkles, every worry line, every laugh line on her face, was shared with you. Every grey hair on her head is a symbol of patience gone wary with you and your children, every beat of her heart is strong with the commitment of 40 years. If you can't look at your wife, and know that you two made a commitment all that time ago, then you have no heart. You have no way of being able to tell yourself that you love her, because love, doesn't just leave after so long. I am sure you could have some fun but that other woman, nothing on her body marks her dedication to you, not a single thing and she should be ashamed for not putting a stop to this. She might as well be looking at your wife and telling her "Oh well, it doesn't matter that you have been with him all these years and gave him his children, I am younger and more beautiful than you will ever be." If she was a stranger talking to your wife like that would it make you mad? Would it make you want to protect your wife because deep down, she is attacking your life and you are foolish enough to go right with it. It is a humiliating slap in the face and why would you want to do that with your life partner? If you feel like you've lost a connection with your wife, then you need to work on it, you need to take the time and find new things to do with your wife, find that spark because no one is married for that long based on nothing. Forget the other woman and love your wife, enjoy your life, and find that appreciation for her again, she deserves that and your respect as a woman.
If you do go through with this, then shame on you. Shame on you for throwing away someone who loved you in your worse moments, and darker times. That woman who is your wife, is a wonderful lady and with this nonsense, should have never married someone so undeserving of her affections.
“I was never really insane except upon occasions when my heart was touched.” ― Edgar Allan Poe
Wish for a pile of shit to turn into gold hard enough and guess what? It's still a heaping pile of shit.