I want to point out that while "S.A." does invite slashy speculation (and rightly so), I've read much to suggest that this does not refer to our dear Ali, who was a composite character devised for the movie (sure there were plenty of Sherif Ali's out there, but this one shares a lot of Feisal's role, later given back to Feisel in A Dangerous Man: Lawrence After Arabia). The most convincing argument I've heard is for a friend (named Salim Ahmed) from an archeological dig TEL was on before the war.

Just wanted to provide that tidbit--hope it doesn't spoil anything for you! Doesn't stop me from my wild speculations about the characters played to such perfect tension in the film!