I mean the following in the nicest way possible. I do not mean to sound harsh, but it will probably sound that way to you anyway.
Golden R hit the nail on the head when he said to "Gray Rock" her. If you don't know what that means, you can either look up the Hard 180 here in the Healing Library, or else Google it.
It will do one of two things.
It will make her see that you are indeed the Prize and you aren't going to be pushed around and disrespected any longer.
She does not respect you now. Probably hasn't for a long time. If she sees you aren't going to take her bullshit any longer she might, just might, begin to respect you as a man.
The other thing it might do is convince her to go ahead and leave you if that is what she intended to do.
As long as you Simp around her and do the "Pick Me Dance" for her she will disrespect you even more and just stick around to see how long you will grovel for her. That will build up her ego and destroy yours even more. I saw my brother do that with his cheating wife and it was pathetic. Don't do it any more, please.
Please remember that, if you were as bad as you say you were, she had dozens of other options available to her, including just divorcing you. Adultery is the nuclear option to destroy a marriage and the worst option. She denied you sex for years and then gave it to another man.
Stephen Covey had a book a number of years ago titled "7 Habits of Highly Effective People". One of those habits is to begin with the end in mind. In other words, decide exactly what you want and then work backwards listing the steps necessary to try to get to that goal. I know it is hard to think now because your emotions have taken over your life. However, if you can try to think in a strategic manner you might find a little light at the end of your tunnel.
It may be that divorce is the best outcome for your marriage. I know you think your life would be over, but that rarely happens. You would probably end up meeting someone better suited for you... who knows? Anyway, you definitely need to see a divorce and family law attorney and see what the option would look like for you.
I mentioned my brother who was doing the "Pick Me Dance". A younger brother literally grabbed him by the collar and shook some sense into his head. Told him that you can't change a leopard's spots... she is what she is... a cheater... and why would he want to be married to a cheater and be a Plan B... or words to that effect.
My other brother then took him to see a divorce lawyer and got the ball rolling. He had been married 22 years and it was difficult as heck for him to file, but he did. Granted they had no children and it made it easier than someone who has children. Anyway she tried to get him to change his mind, but he stuck to his guns. He ended up with a much better suited woman who had morals and integrity for the last years of his life. He ended up reasonably happy after a few years.
Sometimes you will see it said on this site that you have to be willing to lose your marriage in order to save it. After my sister-in-law tried to come back when he filed for divorce he saw her for who she really was and he no longer wanted a marriage with her.
Cooley said something for you to think about. Is it possible that a lot of your depression was caused by your wife and her denial of sex and other actions?
Again, I mean all of this with kindness even if it doesn't sound that way. Imagine I am your best friend and I am trying to shake some sense in your head and get you see the bigger picture if possible.
The best of luck for the outcome of your situation.