I don't get why she thinks your lover isn't also your best friend. Are her parents an arranged marriage or something?
I stopped following this series a couple of chapters ago, I just enjoy reading comments without seeing the actual manga, so it's probably completely out of context...
...but I think it's very optimistic for you to assume that everyone's parents in real life get along well. If anything, anecdotally lots of people I know were saying something to the effect that their parents can't stand each other, and I think it's pretty well established at this point that lots of marriages don't end well :P