You can't change the past and that realization alone can be crushing, but thinking about what could of have been is not doing you any favors.
You really don't know for sure what would have happened. Appearances can be deceiving. She could have been just as likely to cheat. You are latching on to the "idea," of her. The consequences from choices that were made in the past that can't be undone.
It goes without saying that your W has done the same thing. It can never be changed once it has been acted upon. You still have choices and any choice you make will have consequences. Some are good at first and some are bad at first and bad ones ultimately turn into good ones as your perspective changes. That is just life.
I had an XFiancee that cheated on me. So when I began to date again and met my current W. I valued fidelity. She was good, M material and to be honest was not as attractive as my previous fiancee.
In some deluded way I thought that made me safe. The trouble is we ca never control any one else's actions. Yes we can influence them, but control is not something we can exert over another.
Trying focus less of what you could have done different to make yourself happy and focus more on what you can do today.
I know living in now sounds cliched and I would caution you that we still learn important lessons from the past, but don't confuse what you can learn from the past with what you have the ability to change today.
I know this sucks, but I promise you that this thing does work. Think of bad/missed experiences as teachable moments not drift into a fantasy of what could have been. It just makes the pain worse and saps your will to live.
DS 6, DD 12
Dday 8/31/11. EA/PA. Lied to for 3 years.
Every truth comes to light in a long enough timeline.