You need to open your mouth and start communicating. A lot of boundaries get crossed in sex, it feels great when you’re doing it, but afterwards it can turn hellish.
People’s understanding of your opinion towards them can suffer a lot of anxious twists and turns. Ladies will think that guys will think of them as whores, guys will worry that their performance wasn’t good enough and you just want to get rid of them now. So you should allay those fears.
Second, you need to be thinking really hard about whether you want a relationship with them. It’s okay to be confused and not at all sure yet. But figure it out fast.
If you don’t want a relationship, the second thing to decide is if you still want to keep having sex. If you don’t want a relationship, and don’t want to keep having sex, and you’re a female, and he’s a guy, (jeez, why couldn’t you just put your respective genders in the question?) then you need to be aware that he may not want to be friends with you anymore. Not saying it’s right, but that’s just what it is.
If it’s any other case, then you should be able to maintain a friendship. Hopefully.