People’s experience shows, ending the casual relationship is harder than ending the serious one. It’s because you really match in a bed and it brought you together more than once.
But we shouldn’t be fooled by our sexual compatibility. If partners do not match in other areas or have other reasons to end the casual affair, it should be done without a hesitation.
If you had some kind of emotional attachment though, find the words that would explain your decision. It can be the description of your upcoming long trip or possible family problems.
Some folks don’t want to sound like schoolchildren when they find excuses, so they say directly they’re done with this affair or this person. Just remember ghosting is never recommended.
It makes your casual partner think there’s smth temporary and your attention can be re-conquered, or, on the opposite, they failed too hard for talking to them. Be nicer with your sex mates.