Cohabitation and Dependent Children Legal Issues.

Yep.  Civil marriage is secular, but it has been so screwed up by religious BS that it is time to scrap it entirely.  Forget the term marriage as it has been focused on "Leaving her father and cleaving only unto her husband." for so long that people think it is a sex permit.
 
These days there is no need for a sex permit.  People have sex.  It is none of the state's business who has the right "To do what, and with which, and to whom."  Anon, Limericks Unlimited.  

People may wish to create a household, sharing assets and income and having certain rights and obligations under common law and tradition.  The state might wish to issue a cohabitation agreement loosely based on marriage law to facilitate these arrangements.  Such an agreement would not cover dependent children. 

People wishing to take on responsibility for dependents either through procreation or adoption would be subject to traditional family law, administered by the state, and hopefully reworked for the benefit and protection of the dependents.  Pretty much ignoring the cohabitation status of the responsible adults.
 
DUO you probably recognise a situation from the old boards where a lesbian chose to have a child naturally with a gay father who lived separately but shared parenting and financial responsibility for the child.  A state that can't deal with that situation shouldn't be in the marriage business.