Look at SWTOR, they managed to put player/npc romances in their game and it works great. It's a nice side element that doesn't distract you from the main story line and actually helps you. As you companions like you more they complete tasks faster and do a better job. And once they like you enough you can start a romance with them. On one of my characters I married one of my companions and now she sends me something every day or so. There is a function to it an it does enhance game play. No player on player romances though, that's just a bad idea.