You already know the answer. The question is do you think your wife and marriage is worth fighting for. If you do, you and her will have to communicate (not the nice platonic things she is giving you) and regain the trust (which means one of them will probably have to leave). When I say communicate, I don't mean you have to go into the details of what occurred in the past. The past doesn't correct the present, but it could destroy the future. Your conversation has to be built around bringing your marriage back to when you were first attracted to each other. . I heard it said that relationships work when we focus on the 90% of things that people do right and they break down when we begin to focus on the 10% that we don't agree with. Somewhere in your relationship, I am sure this is true.
If it is too much work or you are not willing to fight, get a divorce.
You can play the game that he is a "Boy" if you want too, but there are a lot of women that enjoy the younger guys for their own reasons. If your sex life went cold, you know the reason for that also.
In life we attract everything that occurs (good and bad). Whether we understand it or not. Whether we believe it or not. You have to start focusing on what a good relationship looks like. The right person will show up and it may not be your wife. I know when we put a lot of time into something we think that it would be wasted if we walk away. If you learn the lessons that were presented in the marriage, it is actually growing, maturing and moving on. I am not for divorce, but sometimes it is the solution.