Did the man lock up his 6-year old son at home overnight? (把6岁大的儿子一个人锁在家里整整一夜) This question is about 后来才知道 in the following sentence:


  他为了帮我，把6岁大的儿子一个人锁在家里整整一夜，彻底感动了我，交往不到一年，我们结婚了。
  ... bǎ 6 suì dà de érzi yīgè rén suǒ zài jiālǐ zhěngzhěng yīyè ...
  嫁给离婚带孩子的男人 我的生活只剩下两个字, guaixun.com


I translate this to something like:


  To help me [为了帮我], he took his 6-year old son [6岁大的儿子] and locked [锁] him in the house [在家里] by himself [一个人] for the whole [整整] night [夜], which thoroughly [彻底] touched [感动] me, and being in contact [交往] for less than a year [不到一年], we married [我们结婚了].


This seems like a peculiar sentence: it seems the man locked up his 6-year old son at home overnight, and the woman (who wrote this article) thought this behavior was so great that she felt "touched".

I'm surely misunderstanding it.

Question: Did the man lock up his 6-year old son at home overnight?
Your understanding of the sentence is correct. The man in the story did lock his six years old son alone at home for entire night so that he could help a woman. 

The writing of that woman illustrated she is a self centered person. And the man was a horrible father.

Side note:


  Around 1997, I watched in the news in Hong Kong that there were two working parents who kept their two preschool age children locked in at home during their working hours, because they couldn't afford daycare. Unfortunately, a fire broke out in that apartment and the two kids couldn't escape  because the door was locked and were killed in the fire. The parents felt so guilty, they hanged themselves within few days.


That's why I feel so strongly about locking kids at home by themselves-- Nothing worth the risk!