It seems from the Chronicle of Ernoul that he was supposed to marry an heiress, Cécile Dorel, the niece of Raymond III of Tripoli. I told the story (in "The Power of Gold") of how he lost her because of 10,000 bezants. After that incident, Gerard fell ill for awhile, then swore off women and joined the Templars.
When Baldwin IV died and there was disagreement in the kingdom over the proper husband for the successor, Queen Sibylla, Raymond of Tripoli (and many others) felt her husband, Guy of Lusignan, was unsuitable, and a search in Europe was conducted to find some else. Gerard, holding a grudge against Raymond, chose to support Guy as king.
After 1187, when the trip to Europe resulted in a donation from King Henry II of England to support the Christian kingdoms in the Holy Land, Gerard took the money designated for the Templars and hired mercenaries to attack Saladin's son, al-Afdal, in the poorly planned Battle of Cresson. They were hopelessly outnumbered and Gerard was wounded. He was also one of the few that even survived.
That was in May. In July he led the Templars into the Battle of Hattin. Hattin was a disaster for the Christians. Saladin had taken the city of Tiberias. Gerard and others wanted to besiege it and take it back. Raymond's advice was to wait and let Saladin leave the strong-walled city to continue spreading his territory. Gerard wouldn't listen to Raymond and wound up on an undefended plain where they were surrounded and captured. Gerard was one of many prominent men taken hostage. Lower ranked Templars were executed.
Gerard was g\offered a deal by Saladin. If Gerard would convince a templar fortress to simply surrender without fighting, Saladin would let Gerard go. Gerard agreed, then did the opposite: he went to Tortosa, a major port on the Syrian coast, and set up its defense. He seized more of the money that Henry II had donated to the Crusader cause (but not specifically given to the Templars). Conrad of Montferrat wrote a letter in September 1188 complaining about this.
Gerard used the money for more mercenaries. He and Guy went to the Siege of Acre, where Gerard was again taken hostage by Saladin. Saladin had little patience with someone who had broken his promise once already, and beheaded Gerard.
The Siege of Acre became a significant event in the history of the Crusades, and though mentioned has never been discussed in detail. We'll take a close look at it starting tomorrow.