Dear Carrie: My boyfriend and I just got engaged. While we agree on most things, we seem to have a lot of differences when it comes to handling money and have had several arguments about it. How can we keep this from becoming an ongoing problem?—A Reader Dear Readers: “How to avoid fighting about money” should be a required class for every couple. No matter how close you are, money differences have a way of creeping into—and causing problems in—the best of relationships. While there’s no lack of studies on money problems as a major cause of disagreement and conflict, the reasons for those problems can be as varied as the couples themselves. But while the particular reasons you and your fiance argue about money may be unique to the two of you, there are some common ground rules that any couple can use to help work out their differences …