Long term relationship means a relationship that last long and both sides have sincere emotion on each other. as a specific long term relationship, marriage involve more beyond it.mariage accumulate the worlds best wishes and hopes. Whatever rains and storms will never break it up. Couples tide over the difficulties they encountered was common ambition and efforts. Marriage can have many difficulties, what counts is the spirits that they will never left each other alone and stranded. While friendship can also mean long term relationship, but it isn't as glorious as marriage. 

As my observation between the long relationship and marriage people, I think it is important that you need jump out the definition of the connection  when you in a special connection with someone you love. 
The first and foremost,  you have to make sure you love each other. If not, any connection will not be happy, everybody knows that. 

Secondly, change you mind. The love definition is pure and sincere. Marriage makes a invisible circle. If you drop into the circle, you would be afraid. So, jump out!  When you in a marriage, you could not mind the circle  for you and your lover. The tips will make you have  more fun and happiness in your long long marriage. In the meantime, if you are not in the circle. You could pretend  in a marriage with your love, it can make you have more responsibility for the long relationship and support the relationship be continued. 

I have to say the circle reminds me of the Monkey King 's golden hoop. But the real love doesn't like the Journey to the West. 

The last and the most important, you two love,believe, and honest to each other. 

Enjoy your love life! 

I think a long-term relationship is only between the two, and they will meet or deal with all the difficulties simply  But marrige means the couple need to ge to know each other's family, they also need to try to putting themselves in and being more tolerant of others' inadequacies will undoubtedly create more conflict. 

Marriage is recognised and protected by law, but longterm relationship is not. That's the biggest difference.

“80% of marriages are broke while 80% of long-term relationships turns a life-term” (me)

A successful Long-term relationships as a matter of fact based on trust and compatibility of the two or more people involved voluntarily by a freedom of choice and it truly manifests a real affection, reliability and concordance. Incompatible people will not be able to keep relationships for long.

However marriage doesn’t mean being a long term relationships at all. It can be broke after a month or a year. Marriage is _just and only_ an officially registered _relationships_ which may last long or short. Also Marriage is not a warranty nor manifestation of compatibility. However being legally tied incompatible people in marriage becoming hateful and unhappy, as they have no freedom of just abandon a relationships as they turns into hell.

Marriage is basically outlived itself, it is an outdated institution developed in time when women has less rights then man and marriage laws written to justify that legal rights imbalance. Nowadays women possess equal legal right as a man (and by many outdated legislation in fact their rights overprotected and outweighs men’s legal rights). In such circumstances marriage law becomes an abuse for a man whose rights are less protected at all plus a marriage law absolutely cuffing them into a “legislative slavery”.

Such outdated marriage legislation overprotective to women let them freedom to behave conscientious-less what lead to a prevalence of unhappy marriages and abundance of divorces (80% of marriages are broke while 80% of long-term relationships turns a life-term).