Women love Friends but consider them unfuckable because they are not masculine enough. Women hate Jerks because they are asswipes but fuck them anyway. Thus, every woman in the world fucks Jerks and then complains to her Friend about how badly the Jerk treats her.
Often used with other phases like
"You are like a big brother to me."
"You are such a nice guy." and "It's not you, it's me."
"You are such a nice guy, and I love you as a friend ...... "
"I'm telling you as a friend, you really shouldn't be drinking that much! I'm worried about you!"