A common law relationship is different from a legal marriage.
How ever in recent years the legal system is treating some unions similar to a legal marriage when it comes to separation of assets. Laws and the judicial system vary in different countries. The length of the relationship and complexity can see both parties involved having an equal share in asset division or not. Some people choose to have a prenuptial agreement before living with each other to protect assets they bring to the relationship. The percentage of common law unions has greatly been increasing and the courts are dealing with more cases all the time. Financial responsibilities for children born in a common law marriage are similar to a legal binding marriage.
The legal term "unjust enrichment" must be proven. There is no clear rules and proving can be very time consuming and expensive. Every state / province in USA and Canada have different rules. Ultimately the judge in a legal dispute will have the final ruling. This can be appealed and taken to supreme court. Be prepared to have large legal costs if an agreement can not be concluded in a civil court. It is generally better for the parties to reach an amiable agreement with out the courts being involved. Any financially gain supposed could be quickly lost in lawyer fees.
In a legal marriage you can have a court order stopping depletion of assets. In a common law separation there is no such protection. If applying for spousal support you must file with-in 2 years of separating. This still does not guarantee you will receive support.
In the case of death with out a will, there is no automatic enrichment in a common law union. A claim must be submitted against your partners estate.
Basic rules for common law separation:
Both parties keep what they brought to the relationship. Bank accounts and real property in their name. They are responsible for their own debt they had when the relationship started. A good tip is to keep a receipt for everything you have purchased. If assets are in both parties name, then one must buy the other out or the asset sold and divided equally.
Note: Common-law relations are excluded from the provisions of the Family Law Act (Canada) that govern division of property. To protect yourself from the burden of proving shared assets, a cohabitation agreement should be in place before living together.