Stay in an unhappy marriage for your kids?

According to a survey by a parent magazine, only 20% of American parents will keep themselves in an unhappy marriage just for kids' sake. 
As far as I can imagine, this number may at least double in China. 
Two reasons: One is the culture of 100 percent devoted love to (biological) children, and the other is the shortage of love for non-biological children.
There is a old saying in China: "Even a vicious tiger will not eat its cubs" or "No one is capable of hurting his own children".  As a culture, most Chinese put kids in the first place in their lives above anything else: work, marriage, personal hobbies.  One of the reasons, is that in Old China, when people got old and could not work, the kids are the only resource they can seek to for food and shelter.  Situations have changed a lot since the retirement, medical care, social security system develop much better in recent years.  However, the culture has not changed much.  Most people devote all their love to the kids, no matte what.  Almost all the parents believe that giving their children a complete home with both of the biological father and mother present is the most important thing to guarantee a healthy psychological and physical development of their children.
At the same time, in most circumstances parents treat kids completely differently depending on whether there is a blood relationship. Usually when people talk about abuse cases, the first question being asked will always be: Is the child biologically related to the mother/father?  Because most stepparents will not care much about their stepchildren, when couples are in bad relationship, the fear of getting a stepmother/stepfather for their children usually prevents them from stepping forward to divorce - the fear of getting their kids into a bad situation is big enough to prevent people end their unhappy marriages. (Having said that, it always surprises me that both situations seem not uncommon in US: Step parents in US get along with their step children while biological parents abuse/kill their kids - both of which are rare in China).
Therefore, usually in China, couples will try their best to avoid divorce if they have kids: they choose to ignore affairs, abuses, lack of love, you name it.  The reason is simple: people believe that the love from biological parents is not substitutable by ANYTHING ELSE.
Now the question is: Will the children suffer more from an unhappy married biological parents or a happy married mom/dad with a stepparent without too much love.
The answer will never be the same in different culture and to different couples.

The story begins

August 13, 2010.  It will definitely be a special day for me. 

The same day ten years ago, I flied 15 hours from the other side of the earth to this completely unfamiliar country.  It was my first international travel, and it was by myself.  That day, when I looked down from my plane before it arrived at S airport and saw the land covered with continuous trees and plantations, I didn't know that I would stay in this country for so long.  I also had no idea that it is the birthday of someone who is so important in my life.

August 13, 2000.  I came to the United States of America, as a first year Ph.D. student.  My plan was to finish my study as soon as possible and fly all the way back.

Well, sometimes, you are not the only one entitled to manipulate your life.

2010年，8月13日。对于我，确实是个特别的日子。
10年前的这一天，我从地球的另一边飞行了15个小时来到这个完全陌生的国家。那是我的第一次跨国旅行，独自一人。那天，当飞机快达到S机场时，我从飞机上看到这片被连绵不绝的树和植物覆盖的土地时，我并不知道我将会在这个国家逗留这么长时间。也完全没有想到，这一天，是一个在我生命里非常重要的人的生日。

2000年8月13日，我抵达美国，开始我的博士学习。我那时的计划是，尽快完成学业，然后飞回家去。

有时候，你并不是唯一能操纵你生命的力量。