Longman Dictionary of Contemporary English
serial monogamy
noun
EXAMPLES FROM CORPUS
▪ 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.
▪ 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.
Wiktionary
serial monogamy
n. The practice of having a succession of (especially short) monogamous relationships with different people.
WordNet
serial monogamy
n. a succession of short monogamous relationships (as by someone who undergoes multiple divorces)