You are assuming that every single girl he has been with is not a nice person.
All these girls fell in love with him and the one that has been within the longest had to hide the fact that she had feelings for him just so he would stay.
She started getting her hopes on their wedding day and she was really angry that he refused to eat with her and let me ask you this question with the other girls do you think the wouldn't want to comfort him knowing his backstory but do you think that he will let them.
I agree she's not your typical damsel in distress but she is Cinderella just instead of dancing they had really great sex.
It's not exaggerating to say that he only for for her because of sex.
She believed she won't be able to fall in love with him based on the fact that she married once in the dreams of her first life and she didn't fall in love with that guy.
She’s most likely a lot like other girls. But just that one who lasted long, she decided to keep it to herself until she was certainly sure he felt the same way with her. And it actually took a long time before that happened. The difference is that, it’s tagged ‘fates lovers’ and that foreshadowing is very heavy. You know what I mean if you’ve read the novel completely.
Also, Hugh falling for her ‘just because of sex’ is Natural Selection. Did you know you can practically find your ‘soulmate’ through your five senses, because the chemical reactions in your body is telling you that the target of your ‘affections’ have an opposite immune system than yours and more likely to produce an offspring with stronger immune system? XD
I really feel that she is no different from the other girls he has been with, she fell for him so quick but if he had not started to care for her because of they are so compatible in bed and just came to have sex with her and leave without any feels for her at all I feel we will realise that she is pretty much like every other girl he has been with