To be clear, I almost always recommend fighting for the marriage EARLY -- for some pre-determined amount of time that you can stomach, post-BD (3-4 mos.?) Once there is an active legal divorce action, it would be very rare that I would recommend that someone "fight for" a wayward spouse.
A lot of it depends on "what do you know, when do you know it, and does SHE know that you know," so it can be more complicated than that, but generally speaking I advocate all of the strong moves (establish boundaries, firewall finances, fight for your marriage, aggressive affair-busting) be done EARLY and POWERFULLY. Over time, if the wayward spouse is still unrepentant and unwilling to end their affair, I'm more of a "RobX/let them go" guy.
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712
