I think you have a responsibility to pay attention and not be willfully ignorant. If you know someone is emotionally invested in you, you can’t fuck them, walk away and be like “Whoa, I never said it meant anything. Unbunch your panties”. And you can’t just avoid thinking about the issue because you don’t want to realize anything that will interfere with your fun. You can’t tell yourself someone isn’t emotionally involved because you wish that they weren’t.
That said, if you are a personally who genuinely casually sleeps around and you have every reason to believe the person you slept with also casually sleeps around then nothing is automatically assumed in terms of a relationship.
I do think you have an implied responsibility towards any children that are created.
I do think you have an implied responsibility to treat the encounter respectfully and not insult dignity of the person you are with by mocking them later or revealing information they wouldn’t want made public.