We live in a throwaway society now and I supopse that goes for relationships too, they are too easily dropped and the willingness to stick with something and work at it has dropped because we don't have to, divorce does not have the social stigma it did previously and women have far more opportunity for financial independence now.
This is a good thing of course as its has freed people from suffering unhappy marriages but I think it also means they no longer have to work at it which is a shame as you have to if you want a happy life together.
But domestic violence, infidelity and all the lesser problems a relationship suffers have existed since time began, it was just a case people often had to suffer them in silence for lack of a way out.
I still maintain genuine love and commitment existed back then as it does now although life is more complicated now which makes it more difficult but we have more freedom in our lives so its a trade off. It comes down to a choice as to what your priorities are I suppose, if maintaining a happy relationship is more important than other aspects of your life it will succeed.
There are happy couples and unhappy ones, same as theres ever been. its just more apparent now as people have the option to get out and start a new life.