Doesn't matter which situation is closer, they're both nothing like a marriage. There are more than 2 ways to think about it. If marriages are like a car, then there's also the option to ditch it and not get a new one. If it's like a critical body part, someone is way too dependent. Also, those relationship advice books focus on minor issues, not one where someone isn't willing to change, and certainly not willing to read a book like that, and instead demands the other just "love them for who they are".