Lur-King said:
There are a multitude of ways to entice characters to each-other, but making an entire romance game? Well that sounds borderline like one of those "Girlfriend/Hentai/Flash/Simulator" flashes you see on Newgrounds. shudder.
But...but...but they make me feel so special! Like someone actually cares! And they make me have too do my underwear laundry more often too. >.>

Just kidding, couldn't resist.
OT: Really I've gotta go with something along the lines of King's response: while you can definitely make romance sub-plots in your game, building an entire game around a romance story would be rather difficult as undoubtedly it really would just turn out to be a "Visual Novel" type of game.
The problem with romance in games is that to pull it off well you need to be able to invoke a true emotional response within the player of the game. One of the first major hurdles you come to is the fact that not all players will like the characters involved in the romance from the start. So you have to go way in depth and throw in a lot of character developement and backstory so that the players will actually care about the characters. If you manage to get them engrossed in your story, then it'll be easier to pull off the emotional response you're looking for with your romance game. However, at that point, the real question is "Why not just go read a romance novel and save yourself some money rather than buying a game?"
That's really why a lot of people didn't like the "romance" options in the Mass Effect series. Personally I'd argue that with the exception of Liara, there really isn't any emotional connection between Shepard and any of the other characters. I mean really? FemShep and Garrus? Just try and defend that as anything but pure fan-service with Mordin giving sexual advice, stating that FemShep shouldn't be giving Garrus blowjobs (ahem, "injest turian protiens") because it could cause mild hallucinations. There's no emotional connection between FemShep and Garrus (while if you stick with Liara through the entire series, you actually can get an emotional connection by the third game, at least in my opinion), it's done really just for the hell of it.
In short, I'd say that romances are best left for well-written subplots. Try to base your game entirely around a romance and you get games like Cathrine with a dude in his underpants running away from a giant ass monster trying to eat him. Oh yeah, THAT'S definitely every Valentine's Day ever all over again.
