Handfasting was a rite which was practiced by the Celts, it was really done as a sort of trail marraige, in which when a couple decdied they wanted to get married, they first would have to go through a handfasting, which got its name becasue the couples hands during the handfasting ceremony were littlered fastned together by a piece of rope.
The handfasting, if I recall correctly would last from beltane to beltane during the period the couple would live together as if they were a married couple, and in that time get a feel for each other, their quirks and how capatable they really are together, and then after the handfasting period is over they would go back to the Druid, and either decide to go ahead with the marriage, or if they ran into any problems or decdied they really were not intended to be togehter could just walk away clean without any hassle or breaking any bounds.