Answer:
When your friends help you whenever required and even go a lil off the course just to help you, there has to be a really strong bond to do so.
When they stand by you when no one supports you (for the right reasons).
When they do not support you for wrong things.
When they give in their best to get back a smile on the depressed face of yours.
When they give you the mental support you need and stand like a pillar in tough times.