Why does the past matter?

"You don't look particularly excited about it." Madam Jiang observed. 

Luna sighed. "Relationships don't always last long. I mean, liking (or loving) each other doesn't always mean much, right?" After all, her own parents had divorced and in such a heartbreaking way even though they were rumored to have been deeply in love with each other. They were still enemies presently, despite the obvious love in each other's eyes. 

What about she and Jiang Xingyu who had not known each other for that long? 

Madam Jiang understood her concern. However, "You cannot judge your relationship based on someone else's. They are not you and you are not them; your relationship would never be like theirs–not even if that person is your identical twin. Just because your parents broke up doesn't mean you and your husband will break up." 

"H-husband?" Luna stuttered in a whisper. She was still talking about "like". How did it morph into marriage in a flash?