One of these women could be romantically linked to a villain, a gangster who sends hired assassins after the PC.
Or, maybe her husband barges in while the PC is en flagrante, and begins to administer a beat. Even if the NPC is a little lower level, if he's armed, and the PC is nekkid, the PC will be at a pretty big disadvantage.
A bribery scheme could be another thing.......maybe one of these women is an agent for the government of another country (other than the PC's native land), and she arranges for their tryst to be noticed by agents working for his own native government. That could put him in trouble with his liege, king, or whatever, to explain why he was sleeping with the enemy. She could even take the opportunity to plant incriminating papers among his belongings.
Maybe one of these women uses the distraction to arrange to have someone come in and steal his stuff.
A woman he beds could be a favourite of one of the members of the pantheon of gods of his world, who becomes jealous, and decides to inflict some good 'ol divine retribution.
One of the women he's with could be the king's daughter, in disguise, enjoying life outside the confines of the palace walls.....and the PC has now been brought to the attention of the king, or the king's vizier or whoever, who has intentions on the princess. Or maybe the kind just doesn't like a peasant sleeping with his daughter, and decides to do something royal to the PC. Something like that could even lead to a few interesting games.....maybe the PC is imprisoned in the King's most secure prison, intended to disappear.....and now the rest of the PCs have to break into the place to rescue him. For the player, he gets to play a follower or other secondary character, or even the princess, for the rescue attempt on his own character.
Maybe one of these women is a body stealer, and he ends up waking up on the wrong side of the sheets.
He could have his reputation trashed by one of the women he beds.....equipment starts costing more, because merchants all dislike him, people scowl at him, dogs growl at him, that type of thing. Maybe one of them claims he assaulted them, and the PC has to defend himself...the penalty being incarceration, or 6 months labour or something.
I'm sure there are many ways you can make this into an interesting character flaw that results in real consequences for his behaviour.
Banshee