So whats the difference between DB and just walking out and saying screw it I'm done and I don't really give a cr#p anymore. Seems like they are the same thing to me.
That's a great question. In the latter, you say "This is who I am, I don't need you anymore." In the former (DBing), you convey "This is who I am, I've realized I don't NEED you anymore, but I still WANT you along with me on my journey," (but I'm not willing to violate my own Boundaries of Personal Integrity just for the privilege of having you along).
Needing a spouse is enmeshment, co-dependent, and NOT healthy. WANTING them is good, and the difference between your two examples.
You want her to be your frosting, not your cake. YOU are your cake, and you have to be okay with that.
"What is best for my kids is best for me"
Persevere = happily being patient over a long period of time