So far as I can tell, William Longespee was not a Cathar. There is aboslutely nothing in his biography that would point to anything but a devout Catholic.
Nonetheless, I think I may have crossed paths with this sect in that particular life and that I might have been on friendlier terms with them than most Catholics at the time, owing to a peculiar quirk of history.
Not only was I lieutenant of Gascony for a while- and therefore active in a region of France where the Cathar faith was well-established- but there is evidence that I was involved in a politically-expedient alliance with them.
It turns out that Raymond of Toulouse- a noble from Languedoc who was at odds with the Pope for his relative tolerance of the Cathars- was an ally of King John during his excommunication and his campaigns in Flanders and northern France (the same campaign as the Battle of Bouvines).
Here’s where it gets interesting: Simon de Montfort the Elder was a major figure in the Albigensian Crusade and was involved in the Siege of Toulouse against Count Raymond. Raymond de Toulouse died in 1222. In 1225, I was beaten back from a failed campaign to re-take the English king Henry III’s possessions in Gascony (and died shortly thereafter). Some time after this, Simon de Montfort the younger (son of the above) briefly overthrew King Henry III. In both cases I served causes opposed to the house of De Montfort and it makes me wonder how the Cathars might have fared had my campaign in Gascony been successful. Or perhaps I might have been roped into a crusade against them just as easily? I tended to choose sides carefully and I switched sides more than a few times during that life.
For now I have the relief of knowing that so far as I can tell, my hands were clean of Cathar blood. I was at worst indifferent and at best, secretly allied with them. That’s one less thing to regret.