Unfortunately, Guy de Lusignan was a bit of a twit, and the Frankish nobility were right to not want him on the throne. He got into a quarrel with the legendary Saladin (not as legendary at the time, but having just fucking united a vast empire taking up much of Turkish-occupied Anatolia and the Arab world, making him a bit of a threatening opponent for a little crusader-state to be picking fights with) and ended up losing everything in the process, including Jerusalem itself, to Saladin, kicking off the (largely unsuccessful, though very eventful) Third Crusade.