Final answer:
James's act of marrying Jane without divorcing his first wife Charlotte is an example of bigamy, which is illegal and different from serial monogamy.
Step-by-step explanation:
James was married to Charlotte for two years. Recently, he married another woman, Jane, without divorcing Charlotte. He has sexual relationships with both his wives. This is an example of bigamy. Bigamy is the act of entering into a marriage with one person while still legally married to another. It is prohibited in most jurisdictions and can carry legal penalties.
In the given scenario, because James is married to Charlotte and subsequently marries Jane without legally ending his first marriage, he is committing bigamy. This is distinctly different from serial monogamy, which is the practice of being married to one person at a time, but having multiple marriages one after the other, often involving legal divorces in between.