Photo from the Kitchen Witch-UK
Marriage for love is truly a modern contrivance. Pre-television era Celts, believed one spouse was pretty much as good as another (the breathing or still warm approach), so marriages were simplified by the practice of Handfasting.
The logistics were simple. Each year at the Lughnasadh festival, men would line up on one side of a high wall, women on the other. At a gate was a space large enough for a hand to pass through. One by one, a hand went in one side, on the other, a hand held on, sight unseen (supposedly). The newly joined couple then tied a ribbon around their wrists (origin of tying the knot). The couple then were considered married and would live together for a year and a day, to see if they were compatible. If all was well - fine, if they found themselves incompatable they arrived at the next year's festival stood back to back and walked away from each other, signifying their marriage was over. Each was then free to get back in line and try again.
As the christian church reached Ireland it worked overtime to eradicate this practice. It must not have been easy, as for over 600 years various church councils, synods and ruling bodies condemned the practice.
Handfasting was legally practiced in Britain until 1753, Scotland and the Channel Islands allowed handfasting until the Revised Marriage (Scottish) Act of 1939.