When two people are in an unbalance relationship there are certainly going to be consequences, but those who are in a relationship with little emotional investment might find they have bitten off too much. They could find their partner becoming clingy as they try to end it, and their own disgust at the person could cloud their observation. They might suddenly find that dealing with obsession is part of the price they will pay because their partner is not willing to give up the relationship.
A person who has let their emotions overrun their common sense will often resort to obsession when the end of the relationship is apparent. Rather than giving their partner an opportunity to make a clean break, they will do whatever is necessary to keep them. It is an unhealthy situation for both partners, but the person who is the object of the obsession can be in physical danger.