I think the first gay character I remember from a movie was the Sal Mineo character in REBEL WITHOUT A CAUSE. It was obvious to me, as a teenager, that Mineo's character was in love with James Dean. I understand that at one point, they considered putting in a kiss between Mineo and Dean, but the studio refused to allow it.
The next film (or at about the same time) would have been CAT ON A HOT TIN ROOF. When I watched that movie, I kept thinking the whole time I was watching it, that Skipper must have been a Hell of a Hot man, if Brick was picking him over an incredible-looking Elizabeth Taylor