Kind of surprises me how people don't understand that grand achievements very often come from very shallow desires, like greed, lust, vanity or jealousy. You don't have to fight for world peace or friends and family in order to get strong - as long as something motivates you, you should provoke feeling that makes you take action, even if it is something as stupid as your own insecurities that make you for example constantly go to the gym and no matter how good you look it is never enough.
If this guy's source of motivation is lust, there is absolutely NOTHING WRONG with it, use it to your advantage! exactly as he did as a motivation for training. Problem begins when he starts thinking only with his dick and his main goal in life becomes getting his dick wet as often as possible, which isn't the case YET and hopefully it will stay that way.