It was supposed to be taken more as a metaphor, not as hyper-specific example about how it's only okay to break promises over money troubles...but whatever, I guess...
I appreciate what you're saying here, but not everyone has the luxury to go through with 'marriage prep', whatever that entails (I'm guessing time, money and/or access to an actual marriage counselor). Although if you feel it should be a mandatory thing that goes hand in hand with a marriage license, that's a whole 'nother banana.
And you say "if either one or both weren't entirely honest" as if it's some kind of shady business deal. We're talking about spending lives together here! It's really easy to 'not be honest' about your feelings and your ability to commit under any circumstance when you don't know how it feels to actually deal with those circumstances yet. Lots of people want to believe that they can do things that they are actually not even emotionally prepared for.
Is it a pretty punk move to leave someone after they get sick or injured? Yeah, sure. Do some people do it because they feel like being married to a sick person is 'icky' and they "didn't sign up for that"? Totally, yes.
But there are other less childish reasons that also make sense. Maybe you developed PTSD during your time trying to pull your partner through this illness, and even now that things are calmer you feel you need to get out of this situation for the sake of your mental health.
Maybe you never felt as strongly about your partner as you thought you did, and watching them deteriorate and become dependent on you made that more obvious to you.
Maybe your partner took the sickness as an opportunity to begin emotionally manipulating you, and if this is how they're gonna act when they're ill, you don't want to be with them anymore even when they're healthy. If I'd ever been in a relationship before, I could probably come up with more....
Mm, now that I think about it...the answer to the question in the title of this topic really depends on how you define marriage. IS it supposed to be a promise to love one another and stay together till death do you part? Or should it be taken more as a pact to make a life together and be happy for as long as you can?
Personally, I think either definition is fine. There's no reward handed out in the afterlife for staying married to your first partner until you died...It's amazing, sure, to see people who've grown old in their love for one another, but I think it's amazing in the same way as it is to see a Nobel prize winner. It's rad, and if it's within your ability to achieve, you should definitely go for it. But it's a bit unfair to expect it from everyone you meet...and behind the scenes, it might not be as amazing as it looks (not every Nobel prize winner used their intelligence for the greater good...hint hint).