It's hard to get an approximate percentage of happy marriages vs unhappy marriages. The unhappy ones put up a happy front. Most unhappy people in marriages do not even tell close family, such as their parents, of the struggles they are going through because what goes on within a marriage is private. The only thing you can judge is by the divorce rate, which is commonly stated as 50% (not sure how accurate this figure is). The divorce rate for Christians is probably lower, but not by much. And, of the group not divorced, there are probably some unhappy ones there as well.