Some seven hundred years ago, affinity meant "relation by marriage." By extension, the proper use of affinity involves mutuality. But that sense of mutual attraction is often absent in contemporary uses of affinity, such as these: "She always had an affinity for growing fruit." "I have an affinity for vintage chairs." "My friend has an affinity for making things out of cardboard." In these examples, "growing fruit," "vintage chairs," and "making things out of cardboard" are passive elements, not active components in a relationship. Better to say "a talent for growing fruit," "a fondness for vintage chairs," "a flair for making things out of cardboard."
In the examples above, affinity is followed by the preposition for. But in formal English, the phrase affinity for should be avoided. The editor Theodore M. Bernstein advised writers to "discard for" and instead "use between, with, or sometimes to."
Here are three sentences that use affinity correctly: "There is a close affinity between Khan's music and that of the Brecker Brothers." "Some people have a natural affinity with children." "Two vaccines containing native proteins with affinity to porcine transferrin were tested."
There is no affinity unless it is shared by both parties.