All human beings are actually born the same. If you look at baby boy he will cry as much as a baby girl (maybe even more!!). The change comes in how we are socialized and assigned gender roles. Remember when you were 3 and you feel down everyone would say pole but slowly as you grew and became 4-5 years if you were a boy everyone would say to you be brave, don’t cry, big boys don’t cry etc. Meanwhile girls are allowed to cry as much as they want.And slowly we begin to associate crying with the other gender. Girls also form closer friendships with fellow girls while boys tend to have more superficial and functional friendships. As a result girls grow up being able to confide in others and boys grow up learning to be ‘strong’.
As puberty and young adulthood set in, different hormones in the deferent genders cause the reinforcement of the socialization I described above.
When the now grown up boy and girl meet in a relationship each has different ways of expressing themselves. This then results in the notion that girls are more emotional than boys.
There is actually an interesting book that you can read that tries to explain the differences between men and women. It is called ‘Men are from Mars Women are from Venus’