I'm pretty sure Eve fell in love with Roarke before she knew that they shared a similar past. She was definetely in love with him by the end of Naked and he didn't tell her about his father in the first book.
Roarke's face fascinated Eve, sure, but not only because he is "pretty". Eve has seen many very good looking men who didn't capture her attention, let alone her heart. Even before meeting him, when she had only seen his photo, Eve saw much more than beauty in it. She saw determination and strengh and that intrigued her.
But I think what made Eve fall in love with Roarke was how he reacted to seeing her weaknesses. He noticed her fear at intimicy and giving up control when they first had sex and he neither reacted by letting her have it her way (no emotions and she stays in charge) nor did he enjoy her fear and used the new found weakness to hurt her. When he noticed how tired and stressed she was, he took care of her, made sure she eats and sleeps, but he didn't see it as a waekness how much she cared for the victims, but he admired her for it. When she told him about her father raping her Roarke showed compassion but no pity. He gently tended to her injuries at the end of Naked (surely something nobody had done before). Eve can let her guard down with Roarke and he reacts with tenderness and love, without losing his respect for Eve for even a minute. He has seen her at her worst - weak and helpless as well as mean and angry. And he has been furious at her countless of times, but he hasn't for one second lost his love and respect for her. And he has never given up on her, never let her down, not even when she tried her hardest to push him away. He is the first person in Eve's life who knows her completely, with all her flaws and he only loved her more for that. I think it's very hard not to love someone who loves you so completely, not only in spite of your flaws and weak spots, but with them (and yes, that's a difference).
"It is important to fight and fight again, and keep fighting,
for only then can evil be kept at bay though never quite eradicated."
“There’s no such thing as winning or losing.
There is won and there is lost, there is victory and defeat.
There are absolutes. Everything in between is still left to fight for."