This is a 'just curious' question, as the situation caused no bother for either party, it was just amusing.
Basically, after even rather vigorous sex, my boyfriend's penis remained erect for over an hour afterwards, without cause; he was fully satisfied and needed no more 'attention', and in fact he was worn out. Thus said, why is it this happened, what caused it? Aslo, it can't do him any harm, cn it?