The first issue with Shakespeare`s Romeo and Juliet is one of anachronism. He was a poet, not an historian, and thus he blends seamlessly the laws and customs of his own period with those of the period and place in which his plays are set, and so in researching historical background to Shakespeare, it`s important to consider both the dramatic date and date of composition.
The laws concerning marriage in the periods were both civil and religious. They prohibit marriage between people who are closely related (laws of consanguinity), require parental consent for men up to a certain age, forbid divorce, and do not consider a marriage fully binding until consummated.
More important than law was custom. Marriages among nobles were normally arranged and if a noble married against parental wishes, he or she could be disinherited.
David Kastan in Companion to Shakespeare's World posits that legal separations were possible, that women were granted bed and board but were not authorized to remarry. In his view, decisions about marriage were made "in conjunction with parents and friends. Preliminary decisions were made by the young people. Yet, in the upper ranks of society, arrranged mariages were the norm but children were generally consulted."