
It usually means he jizzed in you within a few minutes of sex being initiated. Though ‘finish’ by itself a much broader term, so that sentence can have more innocent meanings. But when the context is vague like that, it is usually referring to sex. And “fast” is subjective and can refer to varying lengths of time, but in this context it generally means before the woman has her O
highly aroused and pleased are the usual suspects if we’re talkin secks! if he’s not someone who masturbates regularly that can also increase the chances of this happening due to the thresholds fir arousal/pleasure usually being lower when those pathways haven’t been fired on in a while if that makes sense.