The phrase "casual fling" is correct and usable in written English.
It can be used to describe a brief, informal romantic or sexual relationship without serious intentions.
Example: "They both agreed that it was just a casual fling and nothing more."
Alternatives: "brief affair" or "light romance."
If not, then maybe give it a miss and try looking for a casual fling online.
Then, two years later, she was pregnant again from a casual fling.
Jabu never finds out about a casual fling Steve has at a conference; instead, she comes across a stack of newspaper cuttings about emigration to Australia.
He obsesses that a casual fling with a woman may have left him disease ridden, although he has no symptoms of sexually transmitted diseases.
An easygoing Upper West Side married man (Michael Douglas) responds to Alex's flirtation after a weekend business meeting and has a casual fling.
Ms. Bacon traces Kitty's increasing susceptibility to the temptation of a casual fling with a clarity that reveals the confusion of feelings underlying it.
The movie's young men chase women for sex, and the women appear no less interested in casual flings.
He came in for justified criticism later for his casual flinging of a racket in the second game of the third set that came perilously close to striking the line judge behind him.
Senior government sources said one of the problems emerging from a review of the agency's performance is that a significant proportion of mothers appear to conceive via casual flings and do not even know the father's surname, let alone address, yet the CSA is required to pursue every lead with equal rigour.
When the episodes aired, Silas was angered by Rae's attitude – her desire to use men for casual flings – and realised he could frame Brendan for her murder.
But the rules for casual flings have changed in this modern texting and social-media era where human interactions are far less personal than in the days of phone calls and face-to-face conversations.
