Hello Lickz,
You must have missed some actions for other characters, once you do them these should open up for you, the masterbation scene is at night when you ask Linda to help you and groping her from back in kitchen comes later in the game ... sometimes in your task list, it says that you've done all with that character but task is written in white font, that means that you interaction with that character will occur again, only when text turns red is when you've done all with that character and should wait for the next update ... hope it helps ...