It’s okay! People can sleep with different people without actually being in a relationship with them, in that case they’re basically just different strangers who don’t owe each other anything.
For example, someone can go to a bar, hook up with a girl or a guy, and have sex with them. They never discussed dating or being together, so it’s not considered a relationship, therefore it’s not cheating either. Then that same person could go to a party with friends and friends of friends, sleep with someone there again without discussing relationships, just enjoy the experience itself. And then maybe even go to a sex party! And from there… well, you get the idea ;)
Cheating is when you’re in a relationship with someone and then go kiss, do petting, or have any kind of sex with another person even though you and your partner already agreed that this kind of behavior isn’t allowed.
There are also different kinds of polyamorous relationships. In those, people communicate with each other, discuss boundaries and what’s allowed, and they’re not cheating even if they sleep with different people