You are right. You have totally blown it. Do you seriously believe that setting a boundary of not dating during a separation agreement is blowing it? She slept around on you while she was married and she promised to be with only you then. What makes you think that if she told you she wouldn't date during a separation agreement that she would not lie? She lies and she cheats. This is your reality. Do what she says and leave her alone. The marriage you had is over and you will never have it back. You can only control yourself and your reactions and actions. You can't make her do anything that she does not wish to do. We all have free will. All you can do is be the best you that you can possibly be. You can only work on the things that you did wrong in your relationship and your issues. You can do it! Drop the rope and learn to detach. It will literally save your sanity!
"It is excruciating pain. It is the pain of separation, the pain of loss, the pain of dreams and expectations unrealized. It is the loss and death of a mirage."