As Eddie and Mo'Nique's breakup and makeup shows, friendships between gay men and straight women aren't that different from same-sex friendships or sibling relationships.

CNN: Gay men, straight women: enduring bonds

Samantha Pillion, an incoming freshman at Wellesley College, agrees that Facebook friendships aren't necessarily built to last.

CNN: Facebook eases freshmen fears, fosters friendship

"I won't miss football but I'll miss the friendships I've made, " said Mr Warren, who is 80 next Sunday.

BBC: NEWS | UK | Wales | North West Wales | It's full time for referee at 80

Fashion has a reputation for being cutthroat, but there are friendships and mentorships as well that don't always get their due.

WSJ: Friendships bubble up at NY Fashion Week

These have the virtue of being more clear-cut than friendships (did you sleep together or didn't you?) and thus what is or is not a link between nodes is unambiguous.

ECONOMIST: What maths tells us about us