This might be an extreme example, but did you ever watch videos of some infamous situations, like the Manson family for example? Where you see them shortly after they were caught, and they were still under the “spell”, and then again years later, after they were separated from him and got some counseling, and they were basically like, what the hell was I thinking?
I think when you are in a bad relationship (with whoever- it doesn’t have to be romantic in nature), it’s really not all that different. It’s really, really hard to see the situation objectively if you are in constant contact with a person (or even doing things like stalking social media, where you keep letting the person occupy space in your head). Even if you know things logically, the constant contact really does hinder being able to be truly objective, and to see things for what they are, you know?