Early on in one's youth it is common to confuse "infatuation" with being "in love". Also when we're younger we have not done the introspective thinking to figure out what traits we truly need in a mate to have a lasting relationship. It's the equivalent of shopping without a list. Most of our relationships come about through "impulsive connections" or "happenstance". Until we figure out what we want and need in a mate for life we are doomed to keep (choosing) the "wrong" mates for ourselves.
However the biggest change in this era compared to previous eras has been with regard to women. The women of today have better career/higher income opportunities and more birth control methods. Not long ago a survey by AARP revealed that in the U.S. (women) "initiated" 66% or 2/3rds of all divorces. Clearly the more "options" one has the more "deal breakers" and less crap they're going to put up with. :-)
Seriously though many couples stayed together in the past because of financial hardship they'd experience if they went through a divorce. It was especially hard for women. Today it's not uncommon for some women to earn more money than their mates, have their own 401k or retirement investment fund. They don't need a man to financially take care of them. Women's expectations of men have also changed. In previous eras men came home and were given their space while the woman took care of the household and handled the bulk of child rearing responsibilities.
A lot of today's women expect the man to help keep the house clean, change diapers, and give them a break by taking the kids on outings from time to time while the wife spends time with her girlfriends or go to a relaxing spa. The more options one has the less they're willing to compromise or "settle". Also the sexual revolution increased infidelity opportunities. Better birth control methods made it possible for women to have sex more on par with men.
At the end of the day each of us (chooses) our own friends, lovers, and spouse. If we're not happy with our choices we need to look at selection process.
There are only two ways to experience joy and peace of mind in relationships: we either get what we want or we learn to be happy with what we have.