Actually romantic dinner is up to you to define
The Olive will be the only fine dining you can get in genting and it is expensive!
If you have enough budget, then it will be romantic enough.
If your budget is limited, then look at the option below, but romantic environment need to sacrifice abit.
There are only 2 western restaurant owned by genting which is The Olive and the New Orleans Barbecue. The New Orleans Barbecue is located inside casino, so the price is affordable but it is actually self service. However, in my experience, the waiter come and serve you the main course but your salad, soup, coffee ownself take. So, you can actually act like a temporary waiter and served to your gf
Try to sit by the window side at least got other view to see (if genting is not cloudly) However, I check at the genting website just now and it said the outlet will be closed from 3rd to 17th Nov.
Pizza Factory also served some western food but more on fast food side, you can order some spaghetti or pizza but environment wise not that romantic. Genting have alot of chinese restaurants but eating in chinese restaurant doesn't give the romantic feeling

Last time genting have the italian restaurant nearby the roller coaster track but I think now close down already. There got quite nice food but the environment...abit not romantic because under roller coaster trak but there will be a band play at the nearby lounge.
Conclusion? Eat in KL for romantic dinner is better option as genting have super limited choice