It's not the sex that makes the concept itself unworkable though, it's the emphasis on player-choice influencing the story of the game. It's one of Eva's central selling points.
Sure, that story could probably work fine in a non-game format, but in that case it wouldn't really include the
player-choice aspect which is what people are here for. The only way I could really see the concept working would be with a groundhogday-esque setup as a TV-series, with a time pocket that repeats itself, and no matter what Lena does she always ends up marrying Ian. Then she'd inch closer to a solution each episode while slowly falling in love with him for realz.
That would change the tone of the whole thing though!