How serious does money matters do to your relationship/marriage?

I cannot remember any time when my partner argue about money. We discuss it out like we need some for this and that, but we never quarrel about. With my ex fiancee, I remember the time that we argue about money. But it was not about something we have to spend. The cause of the argument was due to his brother's luxurious need and he was asking money from my ex fiancee. It did not lead us to a quarrel though. We just exchanged our opinion on whether to give the money or not. I told my ex that it is not proper for him to give the money and spend on something out of luxury. He was working hard to save money for his family, then his brother out of being a spoiled brat wants an i touch. I really hate it because I value my ex fiancee's money. I mean, he worked hard for it, and just waste it for nothing.