Not every man gets off, seeing beautiful women (that they like, have interest on) getting fucked by other dudes.
My philosophy is this- If I don't have a chance with girl A, the best case scenario for me would be; that girl A hooks up with another girl.
Let me ask you- would you rather wish to see Kristen Stewart with pattinson or Kristen Stewart with Cara Delevingne.
Also; will you really get off seeing parker or other dudes sexing, up Jessica? Remember, they are not you. If you are a dude, that is weird; friend.