Love has of course everything to do with Happiness.
Love can propel you to the highest levels of ecstasy or throw you down into the darkest pit of agony and despair. And everything in between.

I totally agree with Anthony Trollope and D.H.Lawrence that marriage (or a modern long term partnership) provides the condition for "perfect intimacy" and enriches the lives of both partners with a "deeper freedom" completing one another in terms of emotions.
And 150 or more years ago, when the average life span of a person was around 50 years, the marriage vow of "until death do us part" was an appropriate one for those times.

But the conditions have changed considerably. These days most people live well into their 80s or even 90s and within a generation or two a 100 year life span will be achieved by increasing numbers.
The vow "until death do us part" is now merely an ancient formula which has no longer any relevance in today's world, and it has become very difficult or impossible for many marriages to fulfill.

Many couples these days no longer bother to get married. They keep their names of birth and by doing so acknowledge and accentuate their individuality.

Society too has changed and now accepts divorce as a common occurrence while modern laws provide for easy separation.
Men are no longer the sole bread-winner of the family, which also tended to keep unhappy marriages together in the past.

The much longer life span these days (see adjacent graph) also has a quite dramatic effect on one's sense of well-being over the course of a life time.

After childhood (during which we may be lucky enough to grow up reasonably happy) our genes take control of our lives and direct us onto the important path towards perseverance and evolution of the human species.
We find a suitable Partner, produce children and rear them to the best of our ability, and as a consequence focus during this period on providing the required material resources for this purpose.   The choice of our partner too is largely determined by the preferences of our genes.

As we progress through this gene controlled period of our life, our happiness gradually but steadily declines (as shown on above graph) until it reaches its lowest point, roughly coinciding with the end of our child rearing responsibilities.

At this point in our life the genes, responsible for the continuation of our species, consider their job done and now leave us to our own devices.

Suddenly we are given the opportunity to grow into the person we always wanted to be. Depending on the inherent temperament of each individual, various scenarios are possible.

Continuing with the same partner we had is in some cases a very successful formulae. But for many others it has become a stifling environment where life is reduced to a routine static existence with no real purpose and little, if any, personal growth.

The original partnership may have been very successful to fulfill the gene's dominated period, but it has become counter productive for further individual growth during the second half of one's life.
Many couples therefore separate in order to create time on their own or to search for a new partner to pursue their path of personal growth and happiness.   This, I strongly believe, is a good thing !

The responsibility towards yourself (as I see it) is simple : 'You start to grow from the moment you are born and you should try to continue to grow until the day you die !'

The advise of the ancient philosopher Confucius is also very relevant here :
'Make broad plans and decisions that provide opportunities to grow, but won't pin you down into a static existence.'