There is no duty on either party to pay maintenance for the support of the other.
Although you may sometimes hear the phrase "common law wife" or "common law husband", in law there is no such status. You are either married or unmarried.
The law has changed with the Civil Partnerships Bill in relation to same-sex couples but the position of heterosexual couples living together as man and wife is vastly different to that of married couples or those in a civil partnership.
Despite this many people choose to live together either permanently or for a trial period before marriage and the question then arises as to how the law can help if there are problems in those relationships, particularly: -
The Community Legal Services Direct (CLS) have produced a document called "Living Together and your Rights if you Separate". This leaflet tells you about the law if you are living with a partner but are neither married nor in a civil partnership. It covers both same-sex (gay or lesbian) couples and male-female couples.