The literal translation is "Where thou art Gaius, I shall be Gaia".
This was the vow recited by brides in Ancient Rome. The groom, would reply by saying "Ubi tu Gaia, ego Gaius", which means "Where thou art Gaia, I shall be Gaius"
I believe that this vow has religious connotations, considering Gaia is the goddess that represents the Earth for both Greeks and Romans. And since the Romans were encouraged to have children, probably the vow is also a prayer for fecundity and longevity.
It is interesting to note that sometimes the groom would not attend his own wedding ceremony, for several reasons, but, there had to be a written letter from him, which contained the vow for his bride, so that the marriage was complete.
After the wedding, the bride would become part of the groom's family and would practice his religion.