I know that the Clone Saga was Marvel's last attempt to "unmarry" Spider-Man, and it was a debacle that in some ways still has consequences. It is the measuring stick to which almost every terribly franchise reboot is compared to. It took countless years for sales to recover.
The problem with the anti-marriage people is they make the same mistake as DC has been doing for ages; bending over backwards to appease the fans of the Silver Age while backstabbing the fans of the Bronze/Modern age. That backfired horribly for DC recently and it only may be a matter of time before it backfires on Marvel.
The problem was, so many people hated the marriage that even many writers didn't give it a chance, didn't explore it with innovation; instead they focused on the stress, the tension, the in-fighting. MJ married a superhero, and they had the most boring marriage ever. I've seen middle aged women marry bikers and have more fun with it.
There has to be a point where a character matures a bit, and grows up. Spider-Man being Archie Andrews forever is limiting, and at least Archie never fools his fans with "events" teasing changes that are undone. At least those comics are honest about their status quo.
There also has to be a point where...well, how long do comic characters need to court before the company will allow them to do what is natural? Lois & Clark had to wait over 50 years, and that only happened because of a TV show (in fact the writers were told to wait until the TV show lasted a few seasons, and needing to fill space in a way spawned the DEATH OF SUPERMAN storyline).
If Marvel wanted Peter & MJ split, they should have realized the roots of the character are in reality, and had them divorce. Over 50% of American couples do. It would have been emotional, real, controversial and fresh. Instead, they went for a standard melodramatic comic piece of baloney. It was so...DC.