Research suggests that promiscuity is not associated with increased happiness and, in fact, that the number of sexual partners needed to maximize happiness is exactly one ... People who cheat in marriage (10% of the married people in the sample have had sex with more than one person in the previous year) are less happy. Men who use prostitutes are also less happy. That is, promiscuous people are less happy

The obvious question: Which way does the correlation go?

One possible explanation is "cheating will make you unhappy, e.g. because it will ruin your relationship", other possible explanation is "people who are already unhappy in their relationship are more likely to cheat".

Money may bring you happiness, but it won’t buy you more sex.

Again, the obvious question is: Does this control for the time spent making money?

One possible explanation is "people are actually not influenced by the money you have when they consider whether to choose you as a sexual partner", other possible explanation is "the more time you spend at work making money, the more money you have, but the less time you have for finding and maintaining sexual relations".