Here are the  two words, compiled from online and personal collections

to describe love, desire and relationships that have no real English translation, but that capture subtle realities that even we English speakers have felt once or twice. As I came across these words I’d have the occasional epiphany: “Oh yeah! That’s what I was feeling...”  For me, thought,it’s the fact that these words generally point to a moment so potent that yet subtle that no single English word can possibly sum it up.It’s the potency and subtley, of course, that I find beautiful.

La Douleur Exquise (French): The heart-wrenching pain of wanting someone you can’t have. When I came across this word I thought of “unrequited” love. It’s not quite the same, though. “Unrequited love” describes a relationship state, but not a state of mind. Unrequited love encompasses the lover who isn’treciprocating, as well as the lover who desires. La douleur exquise gets at the emotional heartache, specifically, of being the one whose love is unreciprocated.

Yuanfen (Chinese): A relationship by fate or destiny. This is a complex concept. It draws on principles of predetermination in Chinese culture, which dictate relationships, encounters and affinities, mostly among lovers and friends.

From what I glean, in common usage yuanfen means the "binding force" that links two people together in any relationship. 

But interestingly, "fate" isn't the same thing as "destiny." Even if lovers are fated to find each other they may not end up together. The proverb, "have fate without destiny," describes couples who meet, but who don't stay together, for whatever reason. It's interesting, to distinguish in love between the fated and the destined. Romantic comedies, of course, confound the two.