I agree with Chaski. Don't become what you behold. Be better than that.
If she's cheating on you, then she can't expect your loyalty and devotion as of right. You're legally and morally justified in making a break with her.
But do it the right way. Tell her that you intend to divorce her, and why. But once you've made the decision you must be firm and resolute in taking it all the way.
She may try to persuade you to give your marriage one more try. She may promise to be faithful in the future. Whether or not you accept that is up to you. Nobody can make that decision for you.
Nobody ever said relationships were easy. Goodness knows, my wife and I have had our ups and downs. Show me a couple who say they've never had a cross word and I'll show you a couple of liars.
You're not unique in your difficulty with your wife. There is nothing new under the sun. Some relationships recover, some don't. No one answer fits all. It's down to the people involved to resolve the issue or make the break.
I wish you the very best of luck.
As for this younger woman. Well, there is no reason why an age difference should prevent you from having a relationship. Many such relationships work brilliantly, although on balance, it has to be said that just as many don't.
You could have a really great time together..... for a time..... but what happens if she meets a man (or woman) of her own age and decides she wants to be with them..? What then for you..?
So.... whatever you do with this girl / young woman, do it with your eyes open. you may have found "the one" and your life together may be wonderful and long lasting. That's worth taking a risk for, isn't it...?
On the other hand, you may just have a wild time for a few months and then she moves on. Another heartbreaking departure for you, but look on the plus side.... It sure will have been wild for a while, eh...? Better to live one day as a lion and all that.
I wish you luck. Nobody on here can give you definitive advice. We can only chip in with our two bobs worth and then wish you the very best of luck.
Bottom line: It's your call. Only you can make it.
A very well thought out post. Thank you.
Taking my time, but to feel that spark again is very nice. I am alive again at least as I have just been maintaining and not living. I don't know what will happen in the end yet, but, yeah it seems I know.