The problem isn't that Homer and Marge get into fights during their marriage, not every couple is going to be perfect and sometimes they'll have serious issues to work with. That's not the issue. What is the problem is that, not only is the "Homer and Marge have a marriage crisis" plotline far too overused now(which makes it come off like the writers don't know what to do with their relationship anymore), but there all virtually the same now: Homer acts a crazy asshole for 20+ minutes and Marge almost leaves him, until he gives one measly apology at the end and she completely forgives him regardless of whatever horrible actions he's committed, or in some cases, he doesn't even do that and Marge just completely forgives Homer for absolutely no reason. Once in a while, they'll mix things ups and have Marge acting like a crazy jerk for no reason, but its generally about Home being a dick. It's gotten to the point now that whenever they an episode about someone else's relationship, they cut back to Homer and Marge arguing just for cheap jokes about how miserable they are.
At this point, after everything he's done throughout the years, it's almost insane that Marge would still love Homer considering how miserable he makes her, and their doesn't seem to be any real reason she would still stay with him (other then just pity).