How do you form emotional bonds with friends/loved ones?

I am writing a paper on friendships, specifically. I talk about how easy it is to let a friendship go, but also what makes a friendship last and continue to grow.

One of my paragraphs is focused on emotional bonds between people. Well my teacher really likes this concept, but wants me to also include how a person would go about forming this bond, but we can not use personal experience or opinions but we can interview others.

So, what are your thoughts on how to form this special bond with friends; how did you and your close friends develop this connection?

Any help I would greatly appreciate!!