Answer: C. Serial monogamy
Explanation: Serial monogamy is when one is in multiple marital or sexual relations one after the other, but it is always the case that one is with only one person in a marriage or relationship for a certain period of time. This is therefore a kind of monogamy because there is always only one partner until the divorce or breakup, when entering into a marriage or relationship with someone else, also monogamous. It's the practice of someone like Steve in this case, who has been married and divorced multiple times.