There are so many people who has an open relationship or no relationship at all. Some people choose to hang out and nothing more. Because relationship are hard to handle and that give you so many responsibility and so many people don't want that. And this is not something wrong. Just because you are in a relationship doesn't make you right, having a open relationship/just hanging out doesn't make you wrong.
If you consider the actors' positions and perspectives on life, not your own life while watching the series, I'm sure you will be able to look at them without prejudice and understand them.
If you look at it individually or internalize the subject, it will be difficult for you to understand. Everyone has different opinion about love and it doesn't make anyone wrong.
Thank you.
(Normally I don't rewatch dramas that much that is why I gave it 5.)