This is a solid list of ostensible reasons for failing relationships, and will serve well in the absence of a deeper understanding of personal psychology. Introspection (supplemented by the careful observation of others) is the best way to uncover the true causal factors that make the above list of symptoms come to pass.

First and foremost amongst causal factors is the reckless application of attention. At the beginning of a relationship, we tend to pay attention to all the person's desirable qualities, and justify or ignore the rest. As time passes, a reversal takes place if not deliberately mitigated by conscious application of attention. After a while, it seems like everything about the person is all wrong, and all the good qualities you loved before seem like insufficient compensation.

They probably didn't change much fundamentally (though they also probably became reckless with their attention), but you've began seeing them in a darker light by doing the exact opposite of what you used to do before - you now look only at the darkness, and largely ignore the light.

Insecurity is what most relationships are founded upon, and it's a poor foundation indeed. Let's look at an example: What is "infidelity"? It's the person you "love" having a meaningful connection with another person. That's it. The reason why you deem it a disaster is because you weren't involved, and you feel the sting of their attention being placed favorably upon someone else in a way that you unreasonably supposed should be reserved for you exclusively.

It's wholly rooted in insecurity, it's selfish, and it has nothing to do with love. If you truly loved that person, you'd be thrilled that they made a positive connection in their lives. You wouldn't deem it as a threat to your desperate need. But this seems like blasphemy amidst a culture of deep psychological dysfunction.

So you see that many of the problems listed above are merely symptoms, and though treating symptoms is better than doing nothing, it's not a cure for what's really going on. To truly resolve these issues and heal relationships (and the world) each individual needs to do the "shadow work" of exploring their own psychology, rooting out their demons, and enduring the pain of a new birth into a better place. The number of people willing to do this is nigh unto negligible.

Much easier to just say your partner is an asshole and move on to find another person. If you're lucky, they'll fit your dysfunctional mold better and you'll get away with shirking your responsibility for personal growth.

Hard news, but true nonetheless.