One of the predictors of both romantic and platonic relationships is homophyle. Most good friendships that i'm aware of are among people who are within a pretty tight band of what you'd consider socia economic status, generally. We often hear people talk about their spouse or their partner being their best friend. Is that optimal? I am guessing that havin a non romantic, purely platonic best friend and a romantic partner is healthier than just having a romantic partner. The odds of its lasting for the miste life might be higher.