Why would she leave her doormat husband when she can fuck this dude and you are just waiting for her at home thinking about ways to win her back like a softcover romance novel character?

You can't cheat on someone you love or respect and even wanting her back means that you don't require a womans love or respect to be her husband which alone is sad and heartbreaking.

She is of course not going to change anything because that would require her to have 1 ounce of respect or love for you which she already showed you she doesn't.

Cheating is 100% of the time a black and white issue.

If you have ANY self respect what soever you leave. 

If you have ZERO self respect and self worth you stay. 

Period.  End of story.
i
If you have kids its the above X100 because you are dooming your children to make the same mistakes by setting this example of a garbage marriage for them to emulate.  On top of that it shows that the parents would rather have their children pay for their shitty life choices then put in an ounce of effort.

Stay if you wan't but don't expect someone who doesn't love or respect you to start respecting you when its clear you dont' respect yourself.