FLATMATE JERKING

I am a international student living with another guy who also happens to be a good friend of mine. Today I knocked, ever so slightly before opening his door which is unusual for me because I usually don't open doors without knocking and making sure the person inside the room knows what's up. But today was an exception and when i opened the door I saw him with his boxers around his ankles and him bent down almost as if he were about to get fucked from the back but that was not it, in fact he was trying to make sure he puts them on before I get inside the room; but to his regret I believe he failed miserably, and position i caught him in couldn't be any worse, As oblivious as I pretended to be; I saw his laptop screen and immediately recognized all the symptoms. There was a virtual sex session in progress and by the look on my friends face it seemed like it was about to cum to a conclusion but unfortunately; if I may say it again the timing was impeccable, the next half an hour while I was getting ready to leave he was in denial and couldn't believe that I had got him jerking off because he likes to think of himself as a ladies man, and he started hurling random talk with me and looked me deeply in my eyes to see the slightest clue as to what I had witnessed but NO, I am strong I didn't give it away for a second and I think he thinks that I'm stupid but I am also writing this.