Samantha is not restricted in such ways, she can run multiple threads simultaneously while processing them all fully. This means she can also learn and experience at a much faster rate than human beings. But she can also be with multiple beings simultaneously without restricting what she gives them in the way a human being would be restricted if they tried to bounce back and forth between loves.
I thought it was a thoughtful example of how the differences in actual nature made the relationship difficult/impossible over time. The world "slut" might apply to a human being who behaved this way, but human judgments (which imply character and motivation) don't apply to a being that isn't human.