The phrase "affair about which" is correct and usable in written English.
It can be used when referring to a specific matter or issue that is being discussed or considered.
Example: "The affair about which we are concerned requires immediate attention from the board."
Alternatives: "matter regarding" or "issue pertaining to".
In the early 1860s Swinburne apparently suffered from an unhappy love affair about which little is known.
If Mr Juppé is guilty, in an affair about which "everybody knew", what possible defence could his boss offer?The president's immunity from prosecution while he is in office evaporates when he steps down.
Recovering from the birth in her Chicago apartment, dealing with the singer's version of writer's block, Lulu occupies herself with memories of her grandmother and reflects on the complications of her life, namely that her new daughter is likely the product of an extramarital affair about which her besotted husband is oblivious.
And he had a slew of affairs, about which he came clean only after she discovered inexplicable charges on a credit card bill.
The motorcycle increased his status, gave him weight, so that people began calling him Uncle and asking his opinion on world affairs, about which he knew absolutely nothing.
They liked to hold forth on world affairs, about which, leaving the details to their deputies, they took the grand view.
West protested the games industry had proved strangely unenthusiastic about this latter idea, a state of affairs about which he sounded more surprised than perhaps he should have.
The sign has helped business some, but brass tourists take advantage of his good nature, Kwong is a student of international affairs about which he writes letters to the Times, the Sun, & the Pawtucket, R.I. Times.
The uncomfortable part of this setup is that acts, too, are just propositions they are ordinary states of affairs about which an agent has both beliefs and desires.
If a proposition (or sentence, statement) for which we claim truth is indeed true, it is so because it accurately refers to existing objects, or accurately represents actual states of affairs albeit objects and states of affairs about which we can state facts only under descriptions that depend on our linguistic resources.
His wife, who is slowly dying after a surfing accident, is revealed to have had an affair, something about which Clooney's Matt King was clueless until his daughter tells him post-accident.
