for me my marriage began once we made our committment to each other before God, our friends and family and our minister. Even though I was already living in the home before our marriage I kept to myself and he slept with the first wife only until our ceremony. For me, regardless if it is a mono or a poly that is when marriage begins for me.
B
Wow, we had a similar experience! I started out babysitting for the family and then I eventually moved in. Not long after that I married into the family (they called it handfasting at the time to avoid legal problems in California) and he never slept with me before the ceremony. Still, and this is just me, I didn't feel 'married' until the wedding night because where it wasn't legal I could still just walk away with no consequences. Natural sex is what sealed everything for me because after that I felt married.