Eve for Adam and Adam for Eve.

Why God create Eve for Adam and Adam for Eve? 

Obviously the answer would be Genesis 2:18, "It is not good for the man to be alone."

Alone? Most think it is easy to be all alone. Some even think that staying all alone is better, because responsibility is burdensome. However, man can live alone with a community around him. But can he live all alone just as the only living entity in this world? To understand the scenario, let's look at one example. 

In 1984 an Astronaut Bruce McCandless II, flew away from the space shuttle "Challenger", all alone into the space untethered. He flew away 100 meters from the space shuttle, freely floating in the space. Later, when he was asked about his experience of being in space all alone and freely floating, he answered, "it was extremely cold - think about the silence - just think about you all alone in space."

Frightening isn't it?

That's the reason why God created them male and female (Ge.1:27) - one for the other, so that no one will feel lonely.

1Corinthians 11:11 reads, "Nevertheless, in the Lord woman is not independent of man, nor is man independent of woman." 

Picture taken from https://www.nasa.gov/content/images/bruce-mccandless