serial monogamy
From Longman Dictionary of Contemporary Englishserial monogamyˌserial moˈnogamy noun [uncountable] when someone has a series of sexual relationships, rather than one long relationship or several relationships at one time – often used humorouslyExamples from the Corpusserial monogamy• Serial multipartnerism, which can also be called serial monogamy, means having partners one at a time.• Such would tend to be the case where people practice serial monogamy.• As we have seen serial monogamy could put the claims of unquestionably legitimate princes at risk.• Nevertheless the serial monogamy of kings is likely to have had its implications for the rivalries between their heirs.