Well, there is a big difference in the cases you mention. I think the most important thing to have in mind when speaking about a photographer's right is to know if this person take the pictures as a job or for personal reasons.
What you are describing in the second paragraph is exactly that: a stalker. And it is a prohibited activity. So is the second example you propose: a boyfriend that goes to his girlfriend's house with a camera and expects to catch her doing something he wouldn't like in her intimacy is wrong, he is being a stalker.
The case of the paparazzi is different; their job is to tell society, through pictures, something about a case of public relevance. If we are talking about someone who is famous, but the pictures taken invade her/his private life, they can sue the paparazzi and the paparazzi will have to throw the pictures away.
Tyler's case, from 13 Reasons Why is a good example; he was taking pictures of his partners, some knew about it and some others didn't. He should have told everyone what he was doing, otherway, he is also a stalker.
The key here is to know if the photographer is allowed to take pictures or not; if he is not, then the activity is forbidden.