It was understood by the Hebrews, that a married man could have sex with as many concubines or single women as he wished. But if a married women had sex with another man she could be killed, since this violated her husbands property rights. Clearly there was no biblical problem of many wives but marriage was also related to the property concept was also tied to the idea of inheritance - that a man would determine that his sons and only HIS sons would inherit his property. Therefore he had to be certain his wives did not have sex with others. Today, women should have the same freedom as men have always had.
Marriage is mostly for insecure people who feel a piece of paper provides security.
Well, OK, that may be a bit overboard. Marriage also can be important in our culture for children and legal advantages. But the point is it should not just be so artificially make one feel more secure. If you need security you need a better more communicative relationship not marriage. Instead of marriage, why not be together because you love each other and want to be together.