Head-hopping is when the Point of View from which the story is being told, changes inside a scene.
In a very long scene, one such change may be permitted, but it’s better to stay with the same viewpoint for the entire scene if possible.
Headbanging POV shifts are when the author changes POV back and forth and the reader starts to feel like she’s at a tennis match watching the ball go down the court and back up again. This is not good.
Before writing a scene the author needs to decide what part of the story she is telling here, and who knows what she has to describe. If one character leaves the scene part-way through, they cannot know what happens after they leave, so using them for POV won’t work.
A few authors naturally write in Third Person Omniscient POV. That is, they are like a narrator, who sees everything that happens in the world of the story. But unless you're J.R.R. Tolkien or Jane Austen, it’s much better to stick with convention. One scene, one viewpoint.
However, this doesn’t mean one viewpoint per book. It’s important that all the main characters tell part of their story from their own POV so the reader gets to know them intimately, how they think and react, instead of only seeing them through someone else’s eyes. Especially so in ménage stories, if all the parties are to be equal. It’s hard to believe in a happy ever after if one of the main characters never gets to tell the story from their own POV.