I don't think you should do anything about it. Just let him be and continue to be friends. I am glad to hear you still want to be his friend good for you :cool:.
The porn could have just been placed there if he has a sibling(I have no clue).
But I highly advise you not to go snooping around on his computer for more. I think you should respect his privacy, and just let him tell you him self some day if ever that he is gay. Don't ask him about it, and let him do it all him self, it is better that way.
You both will probably appreciate it later, you might not understand why not to look and ask him now but you will when your older.