How do I See Friendship between two people?

You can construct a URL manually....
(note: you have to be friends with both people)
You will need their usernames
(not their real names, their vanity names)

Once you have both vanity names, here is how to construct the URL you need.

(V1 = the first person, and V2 = the other person)

http://facebook.com/V1?and=V2

For example, here's a friendship page with Mark Zuckerburgg (guy using a fake name) and one of his friends

https://www.facebook.com/markzuckerburgg?&and=jessica.porter.9912

But since we aren't friends with both of those people, we don't get to see their interaction.

After you click that link, click on the "more" button in the upper right corner, and you will see two boxes for entering two of your friends' names. You can then just type/tag their names into the boxes to see their friendship.