No....you don't...you need to calm down....he is 19, which is an adult...granted, the tape sounds disgusting, but considering that he is 19 and a virgin, I think you have raised him well.
That tape could be a joke from a friend, and he might have watched a couple of minutes and turned it off in disgust. You would never have come across it if you hadn't been looking for something and innocently found it....give your son wide berth on this...he would be so embarrassed if he knew you knew...it sounds like you have a good kid you should be awesomely proud of!
Do you realize how many men with sons your age are into porn, sex, pot and other things that you really WOULD consider paths of evil?
Women DO fart, my friend, and I think your son was the butt of a joke, no pun intended. Leave this good young man alone, and never let him know you know about this tape.
You should get down on your knees tonight and thank God you have such a good young man to love and share your life with. God has been good to you. So many men who have sons that age have heartache, illegitimate grandchildren, sons in jail or on probation...
And, the next time you see him, in fact, tell him how proud you are of him, and how well he has turned out. It will make him stand a little taller and you both will be glad you said those words.