Ever read 'The Godfather'? Michael Corleone's relationship with Kay is the blueprint for this whole genre. It's not a romance novel, but the romantic subplot is absolutely central to the tragedy. Kay represents the normal, lawful world Michael is supposed to inherit, but he's pulled into the family business partly out of a twisted sense of duty to protect that very world from touching his family. Their love gets eroded by lies, violence, and the immense gap between Kay's morality and Michael's reality. You watch this decent man turn into a monster, and his marriage is the collateral damage. It's heartbreaking because the love feels real at the start, but it's fundamentally incompatible with the life he chooses.
That's the classic literary take: romance as the casualty of crime. It's less about the spicy chemistry and more about the slow, chilling dissolution of a relationship under the weight of power and secrecy. For me, that's often more affecting than any 'mafia boss falls for innocent girl' trope. The romance isn't the fantasy; it's the cost.