In regards to the wife thing. Perhaps I made too much emphasis on Minghui being a lioness, but my actual point was, it's not because Ruoxi was afraid of Minghui or the prospect of being one of many wives, but through that event, she realizes 8th will not protect her or put her first. Remember you said Ruoxi did not understand why she couldn't face death with 8th? Shouldn't you be able to if you really loved someone? Well, I think ti's because the Minghui thing had put doubt in Ruoxi's mind (subconsciously, because I don't think she realizes it.) if she was as important to 8th as she thinks. As a modern woman, I think Ruoxi has that idea that if you love someone, then you'd place them first and protect them with all your abilities. But 8th clearly can't do that.
8th's brushing off of Minghui's bullying towards Ruoxi's sister shows some insincerity what 8th is making his love to be like. Ruoxi knows, that he will do the same if the same thing (the bullying) happened to her; there's no way he'll come to her defense and cross Minghui. For him it's such a minor incident. As Ruoxi explains to 13th, why she didn't fall in love with him, she says that she tends to love those who take that first step to show affection, and who gives a lot to her (love wise). I guess you can interpret that as, the more one loves her, the more she'll love back. Sincerity is a big factor here. Therefore, she didn't love 8th as much because his love wasn't deep enough or sincere enough.