the moon does not fall and collide with earth

Solution

The moon never actually falls on the surface of the earth.

Now, to understand this, we first need to understand the nature of the force between the moon and earth and also the movement of the moon under this force.

So, the gravitational force is the force that acts between the earth and the moon, and the moon moves in the circular orbital due to the centripetal force generated by the gravitational force. 

Similarly, the earth and sun also experience this gravitational force between themselves.

So, yes the moon does fall towards the earth, but the earth also moves in its orbit and covers more distance away from the moon relative to the distance covered by the moon.

 Hence, the moon never falls on the surface of the earth.