I have read that an important aspect of successful long-term marriages is having the mentality that the marriage will be fought for and worked on at all costs. This versus the thought that - Eh well if it doesn't work out we can always get divorced. And I think the latter sentiment is an epidemic as well.
And at least amongst other persons my age, it seems that once that spark of lust and new-love fuzzies wears off, it's a countdown until the cheating or the break-up is announced. The value and love that must develop over loving and being faithful to someone for a lifetime is apparently very difficult to imagine when another newer, more attentive and exciting person comes along to distract us from the goal.
This is my personal opinion only, but I think there are several important aspects to successful long-term marriages that are basically no longer taught to kids as they grow up:
1) The marriage will be fought for and worked on, as if today is the last day you'll spend with your spouse and they could choose to walk out any day. So often I've seen people who get married, think "Well it'll last forever now", and then proceed to let other parts of life distract them from putting effort into the intimate knowledge of their spouse--physically, mentally, emotionally, spiritually. It does not keep the 'zing' of lust/new love in the relationship forever, but if you think of each day as the last day (tomorrow they're walking out and giving up), then each day is absolutely a GIFT and each day is the day you'll make the effort!
2) I think it is against our "nature" to be monogamous and faithful to one person, but it's also against some people's nature to be loving or be kind. It's against some people's nature to not kill!
That doesn't mean we should strive to be "more than our nature." Avoiding theological reasons for now, society values monogamy and faithfulness because it makes the family unit stable. Spouses know who will be there for them, who will provide, who will raise children, who will care for them as they age. Children know who will give them food, shelter, and education. When families are torn apart, it makes the people in the family unstable...which is like a big ripple effect making the society built on family-units unstable.
3) The biggest thing that doesn't seem to be really deeply taught anymore that I can see, that would probably address a bunch of this is commitment. In the 60's the revolution was "free love with no consequences." In the 70's the divorce revolution began and it was kind of cool to be divorced. But back in the 60's and 70's somewhere we dropped the lesson that commitment was valuable and something worth pursuing, and instead picked up "happiness." Whatever made you happy was cool; if you weren't "happy" it was okay to hurt people and leave your family and tear people apart. Well, this is sincerely my personal opinion but that's silly! First, our "happiness" is from within, meaning that other people don't "make" us happy. But second, that just puts the responsibility for "happiness" on someone else and ditches commitment! Okay, commitment and responsibility are not necessarily "thrilling" and don't generate the 'zing' of infatuation, but chasing that 'zing' is not love and it throws commitment out the window!