You're not a single parent if you live together. If you claim you are, that's fraud.
Marriage is a legal mechanism to do accomplish what long term couples normally want to do. Be eachothers next of kin. Inherit from eachother. Be offical parents of the children.
The current sitting government makes new laws. These laws are pretty old, and have little or nothing to do with the current govt.
It sounds to me like your understanding of what a marriage is, ends at the wedding.