There was a time when I didn't really have time to read everyone's back-stories, and I was also growing weary of newbies really not listening to much of the advice anyway (since they're often still shell-shocked from being bombed, and/or fear was crippling them . . . they simply weren't "ready" to hear it yet), and I began just copying-and-pasting the following in nearly all of my first posts to people.
"Puppy's Short Version, All-Inclusive Advice" for Waylayed Spouses Who Just Got Bombed"
1. Get proof (of whether or not there's OM/OW). Hint: There almost always is.
2. Do either:
2a. Aggressive affair-busting (see Allen A's posts over in Infidelity)
Those are the only two things I've seen work. If #1 turns up nothing, then proceed to #2b. And in the meantime, GAL your ass off, and become the better option. Best case, you'll attract them back, and at a minimum you'll become a better person that will be more attractive to SOMEBODY in your next relationship.